On Thursday 15 October 2020 2:11:10 PM IST Christoph Hellwig wrote: > 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? > Ok. I will try to get this implemented. -- chandan
