On Wed, Feb 15, 2017 at 10:11:38AM -0600, Goldwyn Rodrigues wrote: > > I did not understand short writes. Where can I > > get a short write? If you have a write request of N bytes, and you've already wrіtten M of them you return M from the *write system call instead of -EAGAIN. This is standard practice on e.g. sockets. > > > > If I understand correctly, we do add the flag. > > Replying to myself to correct myself. > > On reading a bit more, I figured that we perform > xfs_file_iomap_begin->xfs_iomap_write_direct. At this point we have > already performed xfs_bmapi_read(). So, a check in xfs_file_iomap_begin > should be good enough. So, the flag required would be with iomap flags, > say IOMAP_NONBLOCKING. IOW, we don't need to go all the way to > xfs_bmap_write() and return when imap.br_startblock == HOLESTARTBLOCK. Yes, except that reflinked files with shared extents will also need some additional special casing - for those xfs_bmapi_read can return an allocated extent, but we might still have to perform a block allocation for a write.
