On Sun, Oct 21, 2018 at 1:27 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Sat, Oct 20, 2018 at 11:09:57PM +0100, Phillip Potter wrote: > > Remove switch statement from ufs_set_de_type function in fs/ufs/util.h > > header and replace with simple assignment. For each case, S_IFx >> 12 > > is equal to DT_x, so in valid cases (mode & S_IFMT) >> 12 should give > > us the correct file type. It is expected that for *nix compatibility > > reasons, the relation between S_IFx and DT_x will not change. For > > cases where the mode is invalid, upper layer validation catches this > > anyway, so this improves readability and arguably performance by > > assigning (mode & S_IFMT) >> 12 directly without any jump table > > or conditional logic. > > Shouldn't we also do this for other filesystems? A quick scan suggests > someone should at least look at xfs, ubifs, squashfs, romfs, ocfs2, > nilfs2, hfsplus, f2fs, ext4, ext2, exofs, coda, cifs & btrfs. > I've tried to do that 2 years ago, not even for readability, but to fix a lurking bug in conversion table implementation that was copy&pasted from ext2 to many other fs: https://marc.info/?l=linux-fsdevel&m=148217829301701&w=2 https://marc.info/?l=linux-fsdevel&w=2&r=1&s=amir73il+file+type+conversion&q=b The push back from ext4/xfs maintainers was that while all fs use common values to encode d_type in on disk format, those on-disk format values are private to the fs. Eventually, the fix that got merged (only to xfs) did the opposite, it converted the conversion table lookup to a switch statement: https://marc.info/?l=linux-fsdevel&m=148243866204444&w=2 Some fs maintainers were happy about the initial version, but I did not pursue pushing that cleanup: https://marc.info/?l=linux-fsdevel&m=148243866204444&w=2 Phillip, you are welcome to re-spin those patches if you like. Note that the generic conversion helpers do not rely on upper layer to catch invalid mode values. Cheers, Amir.
