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?
