Fedora lists are hostile to upstream collaboration via cross-posting, so
I can only forward this for your information.

This causes problems with the i686 builders.

Thanks,
Florian
--- Begin Message ---
As far as I can tell, btrfs assigns inode numbers sequentially using
this function:

int btrfs_get_free_objectid(struct btrfs_root *root, u64 *objectid)
{
        int ret;
        mutex_lock(&root->objectid_mutex);

        if (unlikely(root->free_objectid >= BTRFS_LAST_FREE_OBJECTID)) {
                btrfs_warn(root->fs_info,
                           "the objectid of root %llu reaches its highest 
value",
                           root->root_key.objectid);
                ret = -ENOSPC;
                goto out;
        }

        *objectid = root->free_objectid++;
        ret = 0;
out:
        mutex_unlock(&root->objectid_mutex);
        return ret;
}

Even after deletion of the object, inode numbers are never reused.

This is a problem because after creating and deleting two billion files,
the 31-bit inode number space is exhausted.  (Not sure if negative inode
numbers are a thing, so there could be one extra bit.)  From that point
onwards, future files will end up with an inode number that cannot be
represented with the non-LFS interfaces (stat, getdents, etc.), causing
system calls to fail with EOVERFLOW.

For ABI reasons, we can't switch everything to 64-bit ino_t and LFS
interfaces.  (If we could recompile, we wouldn't still be using 32-bit
software.)

So far, we have seen this on our 32-bit Koji builders, which create and
delete many, many files.  But I suspect end users will encounter it
eventually, too.

It seems to me that the on-disk format already allows range searches on
inode numbers (see btrfs_init_root_free_objectid), so maybe this could
be used to find a sufficiently large unused range to allocate from.

Thanks,
Florian


--- End Message ---
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