On Mon 09-05-16 09:55:26, Jeff Moyer wrote: > Eryu Guan <guaneryu@xxxxxxxxx> writes: > > > On Fri, May 06, 2016 at 10:13:39AM -0400, Jeff Moyer wrote: > >> Eryu Guan <guaneryu@xxxxxxxxx> writes: > >> > >> > On Thu, May 05, 2016 at 03:39:29PM -0400, Jeff Moyer wrote: > >> >> I think this code operates on blocks for a reason: we're trying to > >> >> determine if we'll trigger block allocation, right? For example, > >> >> consider a sparse file with i_size of 2k, and a write to offset 2k into > >> >> the file, with a file system block size of 4k. Should that have create > >> >> set or not? > >> > > >> > Thanks for pointing this out! I think 'create' should be 0 in this case, > >> > my test failed in this case, with both 4.6-rc6 stock kernel and my > >> > patched kernel. > >> > > >> > I'm testing an updated patch now, hopefully it's doing the right thing. > >> > It's basiclly something like: > >> > > >> > if (offset < i_size) > >> > create = 0; > >> > else if ((block_in_file >> blkfactor) == (i_size >> (blkbits + blkfactor)) && > >> > (i_size & ((1 << (blkbits + blkfactor)) - 1))) > >> > create = 0; > >> > >> I think that can be simplified to a single check; something like: > >> > >> if (block_in_file < total_blocks_in_file) > >> create = 0; > > > > I may miss something, but this doesn't seem right to me. Still take your > > example, on a 4k block size & 512 sector size filesystem > > ... where blocks are in file system block size units. So: > > if (fs_block_in_file < total_fs_blocks_in_file) Agreed. The test should be: if (fs_startblk < (i_size_read(dio->inode) >> (sdio->blkbits + sdio->blkfactor))) Sorry for not having a look earlier. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
