Re: [PATCH V6 11/11] xfs: Introduce error injection to allocate only minlen size extents for files

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On Mon, Oct 12, 2020 at 02:59:38PM +0530, Chandan Babu R wrote:
> This commit adds XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT error tag which
> helps userspace test programs to get xfs_bmap_btalloc() to always
> allocate minlen sized extents.
> 
> This is required for test programs which need a guarantee that minlen
> extents allocated for a file do not get merged with their existing
> neighbours in the inode's BMBT. "Inode fork extent overflow check" for
> Directories, Xattrs and extension of realtime inodes need this since the
> file offset at which the extents are being allocated cannot be
> explicitly controlled from userspace.
> 
> One way to use this error tag is to,
> 1. Consume all of the free space by sequentially writing to a file.
> 2. Punch alternate blocks of the file. This causes CNTBT to contain
>    sufficient number of one block sized extent records.
> 3. Inject XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT error tag.
> After step 3, xfs_bmap_btalloc() will issue space allocation
> requests for minlen sized extents only.
> 
> ENOSPC error code is returned to userspace when there aren't any "one
> block sized" extents left in any of the AGs.

Can we figure out a way to only build the extra code for debug kernels?



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