On Tue, Jul 27, 2021 at 06:51:54PM -0700, Eric Biggers wrote: > From: Eric Biggers <[email protected]> > > Currently, non-overwrite DIO writes are fundamentally unsafe on f2fs as > they require preallocating blocks, but f2fs doesn't support unwritten > blocks and therefore has to preallocate the blocks as regular blocks. > f2fs has no way to reliably roll back such preallocations, so as a > result, f2fs will leak uninitialized blocks to users if a DIO write > doesn't fully complete. This can be easily reproduced by issuing a DIO > write that will fail due to misalignment, e.g.: > > rm -f file > truncate -s 1000000 file > dd if=/dev/zero bs=999999 oflag=direct conv=notrunc of=file > od -tx1 file # shows uninitialized disk blocks > > Until a proper design for non-overwrite DIO writes on f2fs can be > designed and implemented, remove support for them and make them fall > back to buffered I/O. This is what other filesystems that don't support > unwritten blocks, e.g. ext2, also do, at least for non-extending DIO > writes. However, f2fs can't do extending DIO writes either, as f2fs > appears to have no mechanism for guaranteeing that leftover allocated > blocks past EOF will get truncated. (f2fs does have an orphan list, but > it's only used for deleting inodes, not truncating them.) > > This patch doesn't attempt to remove the F2FS_GET_BLOCK_{DIO,PRE_DIO} > cases in f2fs_map_blocks(); that can be cleaned up later. > > Fixes: bfad7c2d4033 ("f2fs: introduce a new direct_IO write path") > Cc: [email protected] > Signed-off-by: Eric Biggers <[email protected]> > ---
Any opinion on this patch? This really needs to be fixed one way or another. Probably before the conversion to iomap, as this fix will need to be backported. - Eric _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
