On Thu, 8 Nov 2018 03:46:35 -0700 William Kucharski <william.kucharski@xxxxxxxxxx> wrote: > > > > On Nov 7, 2018, at 4:19 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > man 2 lseek says > > > > : EINVAL whence is not valid. Or: the resulting file offset would be > > : negative, or beyond the end of a seekable device. > > : > > : ENXIO whence is SEEK_DATA or SEEK_HOLE, and the file offset is beyond > > : the end of the file. > > > > > > Make tmpfs return ENXIO under these circumstances as well. After this, > > tmpfs also passes xfstests's generic/448. > > As I objected to last week, despite the fact that other file systems do this, is > this in fact the desired behavior? > > I'll let you reread that message rather than repeat it in its entirety here, but > certainly a negative offset is not "beyond the end of the file," and the end > result is errno is set to ENXIO for a reason that does not match what the > lseek(2) man page describes. > > I also mentioned if a negative offset is used with SEEK_CUR or SEEK_WHENCE, > arguably the negative offset should actually be treated as "0" given lseek(2) > also states: > > SEEK_DATA > Adjust the file offset to the next location in the file > greater than or equal to offset containing data. If offset > points to data, then the file offset is set to offset. > > SEEK_HOLE > Adjust the file offset to the next hole in the file greater > than or equal to offset. If offset points into the middle of > a hole, then the file offset is set to offset. If there is no > hole past offset, then the file offset is adjusted to the end > of the file (i.e., there is an implicit hole at the end of any > file). > > Since the "next location" or "next hole" will never be at a negative offset, the > "greater than" clause of both descriptions would mean the resulting offset should > be treated as if it were passed as zero. > > However, if xfstest-compliant behavior is desired, the lseek(2) man page > description for ENXIO should be updated to something like: > > ENXIO whence is SEEK_DATA or SEEK_HOLE, and the file offset is negative or > beyond the end of the file. > > I don't mean to be pedantic, but I also know how frustrating it can be when a system > call returns with errno set for a reason that doesn't correspond to the man page. I think that at this stage we should make tmpfs behaviour match the other filesystems. If the manpage doesn't match the kernel's behaviour for this linux-specific feature(?) then we should fix the manpage. If we find that the behaviour should actually change (and there's a way of doing that in a reasonably back-compatible manner) then let's change all filesystems and the manpage. OK?
