ext4: let setup_new_group_blocks() set multiple bits at a time

[~andy/linux] / fs / ext4 / resize.c

/*
 *  linux/fs/ext4/resize.c
 *
 * Support for resizing an ext4 filesystem while it is mounted.
 *
 * Copyright (C) 2001, 2002 Andreas Dilger <adilger@clusterfs.com>
 *
 * This could probably be made into a module, because it is not often in use.
 */


#define EXT4FS_DEBUG

#include <linux/errno.h>
#include <linux/slab.h>

#include "ext4_jbd2.h"

int ext4_resize_begin(struct super_block *sb)
{
        int ret = 0;

        if (!capable(CAP_SYS_RESOURCE))
                return -EPERM;

        /*
         * We are not allowed to do online-resizing on a filesystem mounted
         * with error, because it can destroy the filesystem easily.
         */
        if (EXT4_SB(sb)->s_mount_state & EXT4_ERROR_FS) {
                ext4_warning(sb, "There are errors in the filesystem, "
                             "so online resizing is not allowed\n");
                return -EPERM;
        }

        if (test_and_set_bit_lock(EXT4_RESIZING, &EXT4_SB(sb)->s_resize_flags))
                ret = -EBUSY;

        return ret;
}

void ext4_resize_end(struct super_block *sb)
{
        clear_bit_unlock(EXT4_RESIZING, &EXT4_SB(sb)->s_resize_flags);
        smp_mb__after_clear_bit();
}

#define outside(b, first, last) ((b) < (first) || (b) >= (last))
#define inside(b, first, last)  ((b) >= (first) && (b) < (last))

static int verify_group_input(struct super_block *sb,
                              struct ext4_new_group_data *input)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_super_block *es = sbi->s_es;
        ext4_fsblk_t start = ext4_blocks_count(es);
        ext4_fsblk_t end = start + input->blocks_count;
        ext4_group_t group = input->group;
        ext4_fsblk_t itend = input->inode_table + sbi->s_itb_per_group;
        unsigned overhead = ext4_bg_has_super(sb, group) ?
                (1 + ext4_bg_num_gdb(sb, group) +
                 le16_to_cpu(es->s_reserved_gdt_blocks)) : 0;
        ext4_fsblk_t metaend = start + overhead;
        struct buffer_head *bh = NULL;
        ext4_grpblk_t free_blocks_count, offset;
        int err = -EINVAL;

        input->free_blocks_count = free_blocks_count =
                input->blocks_count - 2 - overhead - sbi->s_itb_per_group;

        if (test_opt(sb, DEBUG))
                printk(KERN_DEBUG "EXT4-fs: adding %s group %u: %u blocks "
                       "(%d free, %u reserved)\n",
                       ext4_bg_has_super(sb, input->group) ? "normal" :
                       "no-super", input->group, input->blocks_count,
                       free_blocks_count, input->reserved_blocks);

        ext4_get_group_no_and_offset(sb, start, NULL, &offset);
        if (group != sbi->s_groups_count)
                ext4_warning(sb, "Cannot add at group %u (only %u groups)",
                             input->group, sbi->s_groups_count);
        else if (offset != 0)
                        ext4_warning(sb, "Last group not full");
        else if (input->reserved_blocks > input->blocks_count / 5)
                ext4_warning(sb, "Reserved blocks too high (%u)",
                             input->reserved_blocks);
        else if (free_blocks_count < 0)
                ext4_warning(sb, "Bad blocks count %u",
                             input->blocks_count);
        else if (!(bh = sb_bread(sb, end - 1)))
                ext4_warning(sb, "Cannot read last block (%llu)",
                             end - 1);
        else if (outside(input->block_bitmap, start, end))
                ext4_warning(sb, "Block bitmap not in group (block %llu)",
                             (unsigned long long)input->block_bitmap);
        else if (outside(input->inode_bitmap, start, end))
                ext4_warning(sb, "Inode bitmap not in group (block %llu)",
                             (unsigned long long)input->inode_bitmap);
        else if (outside(input->inode_table, start, end) ||
                 outside(itend - 1, start, end))
                ext4_warning(sb, "Inode table not in group (blocks %llu-%llu)",
                             (unsigned long long)input->inode_table, itend - 1);
        else if (input->inode_bitmap == input->block_bitmap)
                ext4_warning(sb, "Block bitmap same as inode bitmap (%llu)",
                             (unsigned long long)input->block_bitmap);
        else if (inside(input->block_bitmap, input->inode_table, itend))
                ext4_warning(sb, "Block bitmap (%llu) in inode table "
                             "(%llu-%llu)",
                             (unsigned long long)input->block_bitmap,
                             (unsigned long long)input->inode_table, itend - 1);
        else if (inside(input->inode_bitmap, input->inode_table, itend))
                ext4_warning(sb, "Inode bitmap (%llu) in inode table "
                             "(%llu-%llu)",
                             (unsigned long long)input->inode_bitmap,
                             (unsigned long long)input->inode_table, itend - 1);
        else if (inside(input->block_bitmap, start, metaend))
                ext4_warning(sb, "Block bitmap (%llu) in GDT table (%llu-%llu)",
                             (unsigned long long)input->block_bitmap,
                             start, metaend - 1);
        else if (inside(input->inode_bitmap, start, metaend))
                ext4_warning(sb, "Inode bitmap (%llu) in GDT table (%llu-%llu)",
                             (unsigned long long)input->inode_bitmap,
                             start, metaend - 1);
        else if (inside(input->inode_table, start, metaend) ||
                 inside(itend - 1, start, metaend))
                ext4_warning(sb, "Inode table (%llu-%llu) overlaps GDT table "
                             "(%llu-%llu)",
                             (unsigned long long)input->inode_table,
                             itend - 1, start, metaend - 1);
        else
                err = 0;
        brelse(bh);

        return err;
}

static struct buffer_head *bclean(handle_t *handle, struct super_block *sb,
                                  ext4_fsblk_t blk)
{
        struct buffer_head *bh;
        int err;

        bh = sb_getblk(sb, blk);
        if (!bh)
                return ERR_PTR(-EIO);
        if ((err = ext4_journal_get_write_access(handle, bh))) {
                brelse(bh);
                bh = ERR_PTR(err);
        } else {
                lock_buffer(bh);
                memset(bh->b_data, 0, sb->s_blocksize);
                set_buffer_uptodate(bh);
                unlock_buffer(bh);
        }

        return bh;
}

/*
 * If we have fewer than thresh credits, extend by EXT4_MAX_TRANS_DATA.
 * If that fails, restart the transaction & regain write access for the
 * buffer head which is used for block_bitmap modifications.
 */
static int extend_or_restart_transaction(handle_t *handle, int thresh,
                                         struct buffer_head *bh)
{
        int err;

        if (ext4_handle_has_enough_credits(handle, thresh))
                return 0;

        err = ext4_journal_extend(handle, EXT4_MAX_TRANS_DATA);
        if (err < 0)
                return err;
        if (err) {
                if ((err = ext4_journal_restart(handle, EXT4_MAX_TRANS_DATA)))
                        return err;
                if ((err = ext4_journal_get_write_access(handle, bh)))
                        return err;
        }

        return 0;
}

/*
 * Set up the block and inode bitmaps, and the inode table for the new group.
 * This doesn't need to be part of the main transaction, since we are only
 * changing blocks outside the actual filesystem.  We still do journaling to
 * ensure the recovery is correct in case of a failure just after resize.
 * If any part of this fails, we simply abort the resize.
 */
static int setup_new_group_blocks(struct super_block *sb,
                                  struct ext4_new_group_data *input)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        ext4_fsblk_t start = ext4_group_first_block_no(sb, input->group);
        int reserved_gdb = ext4_bg_has_super(sb, input->group) ?
                le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks) : 0;
        unsigned long gdblocks = ext4_bg_num_gdb(sb, input->group);
        struct buffer_head *bh;
        handle_t *handle;
        ext4_fsblk_t block;
        ext4_grpblk_t bit;
        int i;
        int err = 0, err2;

        /* This transaction may be extended/restarted along the way */
        handle = ext4_journal_start_sb(sb, EXT4_MAX_TRANS_DATA);

        if (IS_ERR(handle))
                return PTR_ERR(handle);

        BUG_ON(input->group != sbi->s_groups_count);

        if (IS_ERR(bh = bclean(handle, sb, input->block_bitmap))) {
                err = PTR_ERR(bh);
                goto exit_journal;
        }

        /* Copy all of the GDT blocks into the backup in this group */
        for (i = 0, bit = 1, block = start + 1;
             i < gdblocks; i++, block++, bit++) {
                struct buffer_head *gdb;

                ext4_debug("update backup group %#04llx (+%d)\n", block, bit);

                if ((err = extend_or_restart_transaction(handle, 1, bh)))
                        goto exit_bh;

                gdb = sb_getblk(sb, block);
                if (!gdb) {
                        err = -EIO;
                        goto exit_bh;
                }
                if ((err = ext4_journal_get_write_access(handle, gdb))) {
                        brelse(gdb);
                        goto exit_bh;
                }
                lock_buffer(gdb);
                memcpy(gdb->b_data, sbi->s_group_desc[i]->b_data, gdb->b_size);
                set_buffer_uptodate(gdb);
                unlock_buffer(gdb);
                err = ext4_handle_dirty_metadata(handle, NULL, gdb);
                if (unlikely(err)) {
                        brelse(gdb);
                        goto exit_bh;
                }
                brelse(gdb);
        }

        /* Zero out all of the reserved backup group descriptor table blocks */
        ext4_debug("clear inode table blocks %#04llx -> %#04lx\n",
                        block, sbi->s_itb_per_group);
        err = sb_issue_zeroout(sb, gdblocks + start + 1, reserved_gdb,
                               GFP_NOFS);
        if (err)
                goto exit_bh;

        if (ext4_bg_has_super(sb, input->group)) {
                ext4_debug("mark backup group tables %#04llx (+0)\n", start);
                ext4_set_bits(bh->b_data, 0, gdblocks + reserved_gdb + 1);
        }

        ext4_debug("mark block bitmap %#04llx (+%llu)\n", input->block_bitmap,
                   input->block_bitmap - start);
        ext4_set_bit(input->block_bitmap - start, bh->b_data);
        ext4_debug("mark inode bitmap %#04llx (+%llu)\n", input->inode_bitmap,
                   input->inode_bitmap - start);
        ext4_set_bit(input->inode_bitmap - start, bh->b_data);

        /* Zero out all of the inode table blocks */
        block = input->inode_table;
        ext4_debug("clear inode table blocks %#04llx -> %#04lx\n",
                        block, sbi->s_itb_per_group);
        err = sb_issue_zeroout(sb, block, sbi->s_itb_per_group, GFP_NOFS);
        if (err)
                goto exit_bh;
        ext4_set_bits(bh->b_data, input->inode_table - start,
                      sbi->s_itb_per_group);

        if ((err = extend_or_restart_transaction(handle, 2, bh)))
                goto exit_bh;

        ext4_mark_bitmap_end(input->blocks_count, sb->s_blocksize * 8,
                             bh->b_data);
        err = ext4_handle_dirty_metadata(handle, NULL, bh);
        if (unlikely(err)) {
                ext4_std_error(sb, err);
                goto exit_bh;
        }
        brelse(bh);
        /* Mark unused entries in inode bitmap used */
        ext4_debug("clear inode bitmap %#04llx (+%llu)\n",
                   input->inode_bitmap, input->inode_bitmap - start);
        if (IS_ERR(bh = bclean(handle, sb, input->inode_bitmap))) {
                err = PTR_ERR(bh);
                goto exit_journal;
        }

        ext4_mark_bitmap_end(EXT4_INODES_PER_GROUP(sb), sb->s_blocksize * 8,
                             bh->b_data);
        err = ext4_handle_dirty_metadata(handle, NULL, bh);
        if (unlikely(err))
                ext4_std_error(sb, err);
exit_bh:
        brelse(bh);

exit_journal:
        if ((err2 = ext4_journal_stop(handle)) && !err)
                err = err2;

        return err;
}

/*
 * Iterate through the groups which hold BACKUP superblock/GDT copies in an
 * ext4 filesystem.  The counters should be initialized to 1, 5, and 7 before
 * calling this for the first time.  In a sparse filesystem it will be the
 * sequence of powers of 3, 5, and 7: 1, 3, 5, 7, 9, 25, 27, 49, 81, ...
 * For a non-sparse filesystem it will be every group: 1, 2, 3, 4, ...
 */
static unsigned ext4_list_backups(struct super_block *sb, unsigned *three,
                                  unsigned *five, unsigned *seven)
{
        unsigned *min = three;
        int mult = 3;
        unsigned ret;

        if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
                                        EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER)) {
                ret = *min;
                *min += 1;
                return ret;
        }

        if (*five < *min) {
                min = five;
                mult = 5;
        }
        if (*seven < *min) {
                min = seven;
                mult = 7;
        }

        ret = *min;
        *min *= mult;

        return ret;
}

/*
 * Check that all of the backup GDT blocks are held in the primary GDT block.
 * It is assumed that they are stored in group order.  Returns the number of
 * groups in current filesystem that have BACKUPS, or -ve error code.
 */
static int verify_reserved_gdb(struct super_block *sb,
                               struct buffer_head *primary)
{
        const ext4_fsblk_t blk = primary->b_blocknr;
        const ext4_group_t end = EXT4_SB(sb)->s_groups_count;
        unsigned three = 1;
        unsigned five = 5;
        unsigned seven = 7;
        unsigned grp;
        __le32 *p = (__le32 *)primary->b_data;
        int gdbackups = 0;

        while ((grp = ext4_list_backups(sb, &three, &five, &seven)) < end) {
                if (le32_to_cpu(*p++) !=
                    grp * EXT4_BLOCKS_PER_GROUP(sb) + blk){
                        ext4_warning(sb, "reserved GDT %llu"
                                     " missing grp %d (%llu)",
                                     blk, grp,
                                     grp *
                                     (ext4_fsblk_t)EXT4_BLOCKS_PER_GROUP(sb) +
                                     blk);
                        return -EINVAL;
                }
                if (++gdbackups > EXT4_ADDR_PER_BLOCK(sb))
                        return -EFBIG;
        }

        return gdbackups;
}

/*
 * Called when we need to bring a reserved group descriptor table block into
 * use from the resize inode.  The primary copy of the new GDT block currently
 * is an indirect block (under the double indirect block in the resize inode).
 * The new backup GDT blocks will be stored as leaf blocks in this indirect
 * block, in group order.  Even though we know all the block numbers we need,
 * we check to ensure that the resize inode has actually reserved these blocks.
 *
 * Don't need to update the block bitmaps because the blocks are still in use.
 *
 * We get all of the error cases out of the way, so that we are sure to not
 * fail once we start modifying the data on disk, because JBD has no rollback.
 */
static int add_new_gdb(handle_t *handle, struct inode *inode,
                       struct ext4_new_group_data *input,
                       struct buffer_head **primary)
{
        struct super_block *sb = inode->i_sb;
        struct ext4_super_block *es = EXT4_SB(sb)->s_es;
        unsigned long gdb_num = input->group / EXT4_DESC_PER_BLOCK(sb);
        ext4_fsblk_t gdblock = EXT4_SB(sb)->s_sbh->b_blocknr + 1 + gdb_num;
        struct buffer_head **o_group_desc, **n_group_desc;
        struct buffer_head *dind;
        int gdbackups;
        struct ext4_iloc iloc;
        __le32 *data;
        int err;

        if (test_opt(sb, DEBUG))
                printk(KERN_DEBUG
                       "EXT4-fs: ext4_add_new_gdb: adding group block %lu\n",
                       gdb_num);

        /*
         * If we are not using the primary superblock/GDT copy don't resize,
         * because the user tools have no way of handling this.  Probably a
         * bad time to do it anyways.
         */
        if (EXT4_SB(sb)->s_sbh->b_blocknr !=
            le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block)) {
                ext4_warning(sb, "won't resize using backup superblock at %llu",
                        (unsigned long long)EXT4_SB(sb)->s_sbh->b_blocknr);
                return -EPERM;
        }

        *primary = sb_bread(sb, gdblock);
        if (!*primary)
                return -EIO;

        if ((gdbackups = verify_reserved_gdb(sb, *primary)) < 0) {
                err = gdbackups;
                goto exit_bh;
        }

        data = EXT4_I(inode)->i_data + EXT4_DIND_BLOCK;
        dind = sb_bread(sb, le32_to_cpu(*data));
        if (!dind) {
                err = -EIO;
                goto exit_bh;
        }

        data = (__le32 *)dind->b_data;
        if (le32_to_cpu(data[gdb_num % EXT4_ADDR_PER_BLOCK(sb)]) != gdblock) {
                ext4_warning(sb, "new group %u GDT block %llu not reserved",
                             input->group, gdblock);
                err = -EINVAL;
                goto exit_dind;
        }

        err = ext4_journal_get_write_access(handle, EXT4_SB(sb)->s_sbh);
        if (unlikely(err))
                goto exit_dind;

        err = ext4_journal_get_write_access(handle, *primary);
        if (unlikely(err))
                goto exit_sbh;

        err = ext4_journal_get_write_access(handle, dind);
        if (unlikely(err))
                ext4_std_error(sb, err);

        /* ext4_reserve_inode_write() gets a reference on the iloc */
        err = ext4_reserve_inode_write(handle, inode, &iloc);
        if (unlikely(err))
                goto exit_dindj;

        n_group_desc = kmalloc((gdb_num + 1) * sizeof(struct buffer_head *),
                        GFP_NOFS);
        if (!n_group_desc) {
                err = -ENOMEM;
                ext4_warning(sb,
                              "not enough memory for %lu groups", gdb_num + 1);
                goto exit_inode;
        }

        /*
         * Finally, we have all of the possible failures behind us...
         *
         * Remove new GDT block from inode double-indirect block and clear out
         * the new GDT block for use (which also "frees" the backup GDT blocks
         * from the reserved inode).  We don't need to change the bitmaps for
         * these blocks, because they are marked as in-use from being in the
         * reserved inode, and will become GDT blocks (primary and backup).
         */
        data[gdb_num % EXT4_ADDR_PER_BLOCK(sb)] = 0;
        err = ext4_handle_dirty_metadata(handle, NULL, dind);
        if (unlikely(err)) {
                ext4_std_error(sb, err);
                goto exit_inode;
        }
        inode->i_blocks -= (gdbackups + 1) * sb->s_blocksize >> 9;
        ext4_mark_iloc_dirty(handle, inode, &iloc);
        memset((*primary)->b_data, 0, sb->s_blocksize);
        err = ext4_handle_dirty_metadata(handle, NULL, *primary);
        if (unlikely(err)) {
                ext4_std_error(sb, err);
                goto exit_inode;
        }
        brelse(dind);

        o_group_desc = EXT4_SB(sb)->s_group_desc;
        memcpy(n_group_desc, o_group_desc,
               EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
        n_group_desc[gdb_num] = *primary;
        EXT4_SB(sb)->s_group_desc = n_group_desc;
        EXT4_SB(sb)->s_gdb_count++;
        kfree(o_group_desc);

        le16_add_cpu(&es->s_reserved_gdt_blocks, -1);
        err = ext4_handle_dirty_metadata(handle, NULL, EXT4_SB(sb)->s_sbh);
        if (err)
                ext4_std_error(sb, err);

        return err;

exit_inode:
        /* ext4_handle_release_buffer(handle, iloc.bh); */
        brelse(iloc.bh);
exit_dindj:
        /* ext4_handle_release_buffer(handle, dind); */
exit_sbh:
        /* ext4_handle_release_buffer(handle, EXT4_SB(sb)->s_sbh); */
exit_dind:
        brelse(dind);
exit_bh:
        brelse(*primary);

        ext4_debug("leaving with error %d\n", err);
        return err;
}

/*
 * Called when we are adding a new group which has a backup copy of each of
 * the GDT blocks (i.e. sparse group) and there are reserved GDT blocks.
 * We need to add these reserved backup GDT blocks to the resize inode, so
 * that they are kept for future resizing and not allocated to files.
 *
 * Each reserved backup GDT block will go into a different indirect block.
 * The indirect blocks are actually the primary reserved GDT blocks,
 * so we know in advance what their block numbers are.  We only get the
 * double-indirect block to verify it is pointing to the primary reserved
 * GDT blocks so we don't overwrite a data block by accident.  The reserved
 * backup GDT blocks are stored in their reserved primary GDT block.
 */
static int reserve_backup_gdb(handle_t *handle, struct inode *inode,
                              struct ext4_new_group_data *input)
{
        struct super_block *sb = inode->i_sb;
        int reserved_gdb =le16_to_cpu(EXT4_SB(sb)->s_es->s_reserved_gdt_blocks);
        struct buffer_head **primary;
        struct buffer_head *dind;
        struct ext4_iloc iloc;
        ext4_fsblk_t blk;
        __le32 *data, *end;
        int gdbackups = 0;
        int res, i;
        int err;

        primary = kmalloc(reserved_gdb * sizeof(*primary), GFP_NOFS);
        if (!primary)
                return -ENOMEM;

        data = EXT4_I(inode)->i_data + EXT4_DIND_BLOCK;
        dind = sb_bread(sb, le32_to_cpu(*data));
        if (!dind) {
                err = -EIO;
                goto exit_free;
        }

        blk = EXT4_SB(sb)->s_sbh->b_blocknr + 1 + EXT4_SB(sb)->s_gdb_count;
        data = (__le32 *)dind->b_data + (EXT4_SB(sb)->s_gdb_count %
                                         EXT4_ADDR_PER_BLOCK(sb));
        end = (__le32 *)dind->b_data + EXT4_ADDR_PER_BLOCK(sb);

        /* Get each reserved primary GDT block and verify it holds backups */
        for (res = 0; res < reserved_gdb; res++, blk++) {
                if (le32_to_cpu(*data) != blk) {
                        ext4_warning(sb, "reserved block %llu"
                                     " not at offset %ld",
                                     blk,
                                     (long)(data - (__le32 *)dind->b_data));
                        err = -EINVAL;
                        goto exit_bh;
                }
                primary[res] = sb_bread(sb, blk);
                if (!primary[res]) {
                        err = -EIO;
                        goto exit_bh;
                }
                if ((gdbackups = verify_reserved_gdb(sb, primary[res])) < 0) {
                        brelse(primary[res]);
                        err = gdbackups;
                        goto exit_bh;
                }
                if (++data >= end)
                        data = (__le32 *)dind->b_data;
        }

        for (i = 0; i < reserved_gdb; i++) {
                if ((err = ext4_journal_get_write_access(handle, primary[i]))) {
                        /*
                        int j;
                        for (j = 0; j < i; j++)
                                ext4_handle_release_buffer(handle, primary[j]);
                         */
                        goto exit_bh;
                }
        }

        if ((err = ext4_reserve_inode_write(handle, inode, &iloc)))
                goto exit_bh;

        /*
         * Finally we can add each of the reserved backup GDT blocks from
         * the new group to its reserved primary GDT block.
         */
        blk = input->group * EXT4_BLOCKS_PER_GROUP(sb);
        for (i = 0; i < reserved_gdb; i++) {
                int err2;
                data = (__le32 *)primary[i]->b_data;
                /* printk("reserving backup %lu[%u] = %lu\n",
                       primary[i]->b_blocknr, gdbackups,
                       blk + primary[i]->b_blocknr); */
                data[gdbackups] = cpu_to_le32(blk + primary[i]->b_blocknr);
                err2 = ext4_handle_dirty_metadata(handle, NULL, primary[i]);
                if (!err)
                        err = err2;
        }
        inode->i_blocks += reserved_gdb * sb->s_blocksize >> 9;
        ext4_mark_iloc_dirty(handle, inode, &iloc);

exit_bh:
        while (--res >= 0)
                brelse(primary[res]);
        brelse(dind);

exit_free:
        kfree(primary);

        return err;
}

/*
 * Update the backup copies of the ext4 metadata.  These don't need to be part
 * of the main resize transaction, because e2fsck will re-write them if there
 * is a problem (basically only OOM will cause a problem).  However, we
 * _should_ update the backups if possible, in case the primary gets trashed
 * for some reason and we need to run e2fsck from a backup superblock.  The
 * important part is that the new block and inode counts are in the backup
 * superblocks, and the location of the new group metadata in the GDT backups.
 *
 * We do not need take the s_resize_lock for this, because these
 * blocks are not otherwise touched by the filesystem code when it is
 * mounted.  We don't need to worry about last changing from
 * sbi->s_groups_count, because the worst that can happen is that we
 * do not copy the full number of backups at this time.  The resize
 * which changed s_groups_count will backup again.
 */
static void update_backups(struct super_block *sb,
                           int blk_off, char *data, int size)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        const ext4_group_t last = sbi->s_groups_count;
        const int bpg = EXT4_BLOCKS_PER_GROUP(sb);
        unsigned three = 1;
        unsigned five = 5;
        unsigned seven = 7;
        ext4_group_t group;
        int rest = sb->s_blocksize - size;
        handle_t *handle;
        int err = 0, err2;

        handle = ext4_journal_start_sb(sb, EXT4_MAX_TRANS_DATA);
        if (IS_ERR(handle)) {
                group = 1;
                err = PTR_ERR(handle);
                goto exit_err;
        }

        while ((group = ext4_list_backups(sb, &three, &five, &seven)) < last) {
                struct buffer_head *bh;

                /* Out of journal space, and can't get more - abort - so sad */
                if (ext4_handle_valid(handle) &&
                    handle->h_buffer_credits == 0 &&
                    ext4_journal_extend(handle, EXT4_MAX_TRANS_DATA) &&
                    (err = ext4_journal_restart(handle, EXT4_MAX_TRANS_DATA)))
                        break;

                bh = sb_getblk(sb, group * bpg + blk_off);
                if (!bh) {
                        err = -EIO;
                        break;
                }
                ext4_debug("update metadata backup %#04lx\n",
                          (unsigned long)bh->b_blocknr);
                if ((err = ext4_journal_get_write_access(handle, bh)))
                        break;
                lock_buffer(bh);
                memcpy(bh->b_data, data, size);
                if (rest)
                        memset(bh->b_data + size, 0, rest);
                set_buffer_uptodate(bh);
                unlock_buffer(bh);
                err = ext4_handle_dirty_metadata(handle, NULL, bh);
                if (unlikely(err))
                        ext4_std_error(sb, err);
                brelse(bh);
        }
        if ((err2 = ext4_journal_stop(handle)) && !err)
                err = err2;

        /*
         * Ugh! Need to have e2fsck write the backup copies.  It is too
         * late to revert the resize, we shouldn't fail just because of
         * the backup copies (they are only needed in case of corruption).
         *
         * However, if we got here we have a journal problem too, so we
         * can't really start a transaction to mark the superblock.
         * Chicken out and just set the flag on the hope it will be written
         * to disk, and if not - we will simply wait until next fsck.
         */
exit_err:
        if (err) {
                ext4_warning(sb, "can't update backup for group %u (err %d), "
                             "forcing fsck on next reboot", group, err);
                sbi->s_mount_state &= ~EXT4_VALID_FS;
                sbi->s_es->s_state &= cpu_to_le16(~EXT4_VALID_FS);
                mark_buffer_dirty(sbi->s_sbh);
        }
}

/* Add group descriptor data to an existing or new group descriptor block.
 * Ensure we handle all possible error conditions _before_ we start modifying
 * the filesystem, because we cannot abort the transaction and not have it
 * write the data to disk.
 *
 * If we are on a GDT block boundary, we need to get the reserved GDT block.
 * Otherwise, we may need to add backup GDT blocks for a sparse group.
 *
 * We only need to hold the superblock lock while we are actually adding
 * in the new group's counts to the superblock.  Prior to that we have
 * not really "added" the group at all.  We re-check that we are still
 * adding in the last group in case things have changed since verifying.
 */
int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_super_block *es = sbi->s_es;
        int reserved_gdb = ext4_bg_has_super(sb, input->group) ?
                le16_to_cpu(es->s_reserved_gdt_blocks) : 0;
        struct buffer_head *primary = NULL;
        struct ext4_group_desc *gdp;
        struct inode *inode = NULL;
        handle_t *handle;
        int gdb_off, gdb_num;
        int err, err2;

        gdb_num = input->group / EXT4_DESC_PER_BLOCK(sb);
        gdb_off = input->group % EXT4_DESC_PER_BLOCK(sb);

        if (gdb_off == 0 && !EXT4_HAS_RO_COMPAT_FEATURE(sb,
                                        EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER)) {
                ext4_warning(sb, "Can't resize non-sparse filesystem further");
                return -EPERM;
        }

        if (ext4_blocks_count(es) + input->blocks_count <
            ext4_blocks_count(es)) {
                ext4_warning(sb, "blocks_count overflow");
                return -EINVAL;
        }

        if (le32_to_cpu(es->s_inodes_count) + EXT4_INODES_PER_GROUP(sb) <
            le32_to_cpu(es->s_inodes_count)) {
                ext4_warning(sb, "inodes_count overflow");
                return -EINVAL;
        }

        if (reserved_gdb || gdb_off == 0) {
                if (!EXT4_HAS_COMPAT_FEATURE(sb,
                                             EXT4_FEATURE_COMPAT_RESIZE_INODE)
                    || !le16_to_cpu(es->s_reserved_gdt_blocks)) {
                        ext4_warning(sb,
                                     "No reserved GDT blocks, can't resize");
                        return -EPERM;
                }
                inode = ext4_iget(sb, EXT4_RESIZE_INO);
                if (IS_ERR(inode)) {
                        ext4_warning(sb, "Error opening resize inode");
                        return PTR_ERR(inode);
                }
        }


        if ((err = verify_group_input(sb, input)))
                goto exit_put;

        if ((err = setup_new_group_blocks(sb, input)))
                goto exit_put;

        /*
         * We will always be modifying at least the superblock and a GDT
         * block.  If we are adding a group past the last current GDT block,
         * we will also modify the inode and the dindirect block.  If we
         * are adding a group with superblock/GDT backups  we will also
         * modify each of the reserved GDT dindirect blocks.
         */
        handle = ext4_journal_start_sb(sb,
                                       ext4_bg_has_super(sb, input->group) ?
                                       3 + reserved_gdb : 4);
        if (IS_ERR(handle)) {
                err = PTR_ERR(handle);
                goto exit_put;
        }

        if ((err = ext4_journal_get_write_access(handle, sbi->s_sbh)))
                goto exit_journal;

        /*
         * We will only either add reserved group blocks to a backup group
         * or remove reserved blocks for the first group in a new group block.
         * Doing both would be mean more complex code, and sane people don't
         * use non-sparse filesystems anymore.  This is already checked above.
         */
        if (gdb_off) {
                primary = sbi->s_group_desc[gdb_num];
                if ((err = ext4_journal_get_write_access(handle, primary)))
                        goto exit_journal;

                if (reserved_gdb && ext4_bg_num_gdb(sb, input->group) &&
                    (err = reserve_backup_gdb(handle, inode, input)))
                        goto exit_journal;
        } else if ((err = add_new_gdb(handle, inode, input, &primary)))
                goto exit_journal;

        /*
         * OK, now we've set up the new group.  Time to make it active.
         *
         * so we have to be safe wrt. concurrent accesses the group
         * data.  So we need to be careful to set all of the relevant
         * group descriptor data etc. *before* we enable the group.
         *
         * The key field here is sbi->s_groups_count: as long as
         * that retains its old value, nobody is going to access the new
         * group.
         *
         * So first we update all the descriptor metadata for the new
         * group; then we update the total disk blocks count; then we
         * update the groups count to enable the group; then finally we
         * update the free space counts so that the system can start
         * using the new disk blocks.
         */

        /* Update group descriptor block for new group */
        gdp = (struct ext4_group_desc *)((char *)primary->b_data +
                                         gdb_off * EXT4_DESC_SIZE(sb));

        memset(gdp, 0, EXT4_DESC_SIZE(sb));
        ext4_block_bitmap_set(sb, gdp, input->block_bitmap); /* LV FIXME */
        ext4_inode_bitmap_set(sb, gdp, input->inode_bitmap); /* LV FIXME */
        ext4_inode_table_set(sb, gdp, input->inode_table); /* LV FIXME */
        ext4_free_blks_set(sb, gdp, input->free_blocks_count);
        ext4_free_inodes_set(sb, gdp, EXT4_INODES_PER_GROUP(sb));
        gdp->bg_flags = cpu_to_le16(EXT4_BG_INODE_ZEROED);
        gdp->bg_checksum = ext4_group_desc_csum(sbi, input->group, gdp);

        /*
         * We can allocate memory for mb_alloc based on the new group
         * descriptor
         */
        err = ext4_mb_add_groupinfo(sb, input->group, gdp);
        if (err)
                goto exit_journal;

        /*
         * Make the new blocks and inodes valid next.  We do this before
         * increasing the group count so that once the group is enabled,
         * all of its blocks and inodes are already valid.
         *
         * We always allocate group-by-group, then block-by-block or
         * inode-by-inode within a group, so enabling these
         * blocks/inodes before the group is live won't actually let us
         * allocate the new space yet.
         */
        ext4_blocks_count_set(es, ext4_blocks_count(es) +
                input->blocks_count);
        le32_add_cpu(&es->s_inodes_count, EXT4_INODES_PER_GROUP(sb));

        /*
         * We need to protect s_groups_count against other CPUs seeing
         * inconsistent state in the superblock.
         *
         * The precise rules we use are:
         *
         * * Writers must perform a smp_wmb() after updating all dependent
         *   data and before modifying the groups count
         *
         * * Readers must perform an smp_rmb() after reading the groups count
         *   and before reading any dependent data.
         *
         * NB. These rules can be relaxed when checking the group count
         * while freeing data, as we can only allocate from a block
         * group after serialising against the group count, and we can
         * only then free after serialising in turn against that
         * allocation.
         */
        smp_wmb();

        /* Update the global fs size fields */
        sbi->s_groups_count++;

        err = ext4_handle_dirty_metadata(handle, NULL, primary);
        if (unlikely(err)) {
                ext4_std_error(sb, err);
                goto exit_journal;
        }

        /* Update the reserved block counts only once the new group is
         * active. */
        ext4_r_blocks_count_set(es, ext4_r_blocks_count(es) +
                input->reserved_blocks);

        /* Update the free space counts */
        percpu_counter_add(&sbi->s_freeblocks_counter,
                           input->free_blocks_count);
        percpu_counter_add(&sbi->s_freeinodes_counter,
                           EXT4_INODES_PER_GROUP(sb));

        if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG) &&
            sbi->s_log_groups_per_flex) {
                ext4_group_t flex_group;
                flex_group = ext4_flex_group(sbi, input->group);
                atomic_add(input->free_blocks_count,
                           &sbi->s_flex_groups[flex_group].free_blocks);
                atomic_add(EXT4_INODES_PER_GROUP(sb),
                           &sbi->s_flex_groups[flex_group].free_inodes);
        }

        ext4_handle_dirty_super(handle, sb);

exit_journal:
        if ((err2 = ext4_journal_stop(handle)) && !err)
                err = err2;
        if (!err) {
                update_backups(sb, sbi->s_sbh->b_blocknr, (char *)es,
                               sizeof(struct ext4_super_block));
                update_backups(sb, primary->b_blocknr, primary->b_data,
                               primary->b_size);
        }
exit_put:
        iput(inode);
        return err;
} /* ext4_group_add */

/*
 * Extend the filesystem to the new number of blocks specified.  This entry
 * point is only used to extend the current filesystem to the end of the last
 * existing group.  It can be accessed via ioctl, or by "remount,resize=<size>"
 * for emergencies (because it has no dependencies on reserved blocks).
 *
 * If we _really_ wanted, we could use default values to call ext4_group_add()
 * allow the "remount" trick to work for arbitrary resizing, assuming enough
 * GDT blocks are reserved to grow to the desired size.
 */
int ext4_group_extend(struct super_block *sb, struct ext4_super_block *es,
                      ext4_fsblk_t n_blocks_count)
{
        ext4_fsblk_t o_blocks_count;
        ext4_grpblk_t last;
        ext4_grpblk_t add;
        struct buffer_head *bh;
        handle_t *handle;
        int err, err2;
        ext4_group_t group;

        o_blocks_count = ext4_blocks_count(es);

        if (test_opt(sb, DEBUG))
                printk(KERN_DEBUG "EXT4-fs: extending last group from %llu to %llu blocks\n",
                       o_blocks_count, n_blocks_count);

        if (n_blocks_count == 0 || n_blocks_count == o_blocks_count)
                return 0;

        if (n_blocks_count > (sector_t)(~0ULL) >> (sb->s_blocksize_bits - 9)) {
                printk(KERN_ERR "EXT4-fs: filesystem on %s:"
                        " too large to resize to %llu blocks safely\n",
                        sb->s_id, n_blocks_count);
                if (sizeof(sector_t) < 8)
                        ext4_warning(sb, "CONFIG_LBDAF not enabled");
                return -EINVAL;
        }

        if (n_blocks_count < o_blocks_count) {
                ext4_warning(sb, "can't shrink FS - resize aborted");
                return -EINVAL;
        }

        /* Handle the remaining blocks in the last group only. */
        ext4_get_group_no_and_offset(sb, o_blocks_count, &group, &last);

        if (last == 0) {
                ext4_warning(sb, "need to use ext2online to resize further");
                return -EPERM;
        }

        add = EXT4_BLOCKS_PER_GROUP(sb) - last;

        if (o_blocks_count + add < o_blocks_count) {
                ext4_warning(sb, "blocks_count overflow");
                return -EINVAL;
        }

        if (o_blocks_count + add > n_blocks_count)
                add = n_blocks_count - o_blocks_count;

        if (o_blocks_count + add < n_blocks_count)
                ext4_warning(sb, "will only finish group (%llu blocks, %u new)",
                             o_blocks_count + add, add);

        /* See if the device is actually as big as what was requested */
        bh = sb_bread(sb, o_blocks_count + add - 1);
        if (!bh) {
                ext4_warning(sb, "can't read last block, resize aborted");
                return -ENOSPC;
        }
        brelse(bh);

        /* We will update the superblock, one block bitmap, and
         * one group descriptor via ext4_free_blocks().
         */
        handle = ext4_journal_start_sb(sb, 3);
        if (IS_ERR(handle)) {
                err = PTR_ERR(handle);
                ext4_warning(sb, "error %d on journal start", err);
                goto exit_put;
        }

        if ((err = ext4_journal_get_write_access(handle,
                                                 EXT4_SB(sb)->s_sbh))) {
                ext4_warning(sb, "error %d on journal write access", err);
                ext4_journal_stop(handle);
                goto exit_put;
        }
        ext4_blocks_count_set(es, o_blocks_count + add);
        ext4_debug("freeing blocks %llu through %llu\n", o_blocks_count,
                   o_blocks_count + add);
        /* We add the blocks to the bitmap and set the group need init bit */
        err = ext4_group_add_blocks(handle, sb, o_blocks_count, add);
        ext4_handle_dirty_super(handle, sb);
        ext4_debug("freed blocks %llu through %llu\n", o_blocks_count,
                   o_blocks_count + add);
        err2 = ext4_journal_stop(handle);
        if (!err && err2)
                err = err2;

        if (err)
                goto exit_put;

        if (test_opt(sb, DEBUG))
                printk(KERN_DEBUG "EXT4-fs: extended group to %llu blocks\n",
                       ext4_blocks_count(es));
        update_backups(sb, EXT4_SB(sb)->s_sbh->b_blocknr, (char *)es,
                       sizeof(struct ext4_super_block));
exit_put:
        return err;
} /* ext4_group_extend */