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    SubjectRe: [Ext2-devel] [PATCH 2/9] sector_t format string
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    On Thu, 2006-08-10 at 18:37 +0200, Roman Zippel wrote:
    > Hi,
    >
    > On Thu, 10 Aug 2006, Theodore Tso wrote:
    >
    > > Ext4 will support a 48-bit blocknumber format for extents, but I do
    > > want to make ext4 suitable as a general purpose filesystem, and 32-bit
    > > systems will be around for I fear far longer than people might wish.
    > > So while I agree that we shouldn't go _too_ far out of our way to make
    > > things efficient on 32-bit systems, if it's not that much work to
    > > support a 32-bit sector_t, we ought to do it.
    > >
    > > So how about a compromise? We allow for a 32-bit sector_t in ext4,
    > > but we drop the SECTOR_FMT, and rely on %llu and typecasts in
    > > printk's. Then the only other extra hair in the filesystem code will
    > > be a mount-time check to make sure we don't try to mount a large
    > > filesystem on system with a 32-bit sector_t.
    >
    > Thanks, that's what I was hoping for. :)
    > Disallowing to mount large fs without CONFIG_LBD is not a real problem and
    > then also truncation is not an issue anymore (except maybe for e2fsck).
    >

    Just to clarify, the current code (both ext3/4) already check the
    filesystem blocks number before mounting it...it fails to mount the
    large device if sector_t is 32bit:

    in fs/ext4/super.c:

    static int ext4_fill_super (struct super_block *sb, void *data, int
    silent)
    {
    .....
    if (EXT4_BLOCKS_COUNT(es) >
    (sector_t)(~0ULL) >> (sb->s_blocksize_bits - 9)) {
    printk(KERN_ERR "EXT4-fs: filesystem on %s:"
    " too large to mount safely\n", sb->s_id);
    if (sizeof(sector_t) < 8)
    printk(KERN_WARNING "EXT4-fs: CONFIG_LBD not "
    "enabled\n");
    goto failed_mount;
    }
    }
    > bye, Roman
    > -
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