[PATCH] Cygwin: fchmodat: add limited support for AT_SYMLINK_NOFOLLOW
Wed Jan 27 17:26:15 GMT 2021
On 1/27/2021 8:27 AM, Corinna Vinschen via Cygwin-patches wrote:
> On Jan 27 08:22, Ken Brown via Cygwin-patches wrote:
>> On 1/27/2021 7:40 AM, Corinna Vinschen via Cygwin-patches wrote:
>>> On Jan 26 16:30, Ken Brown via Cygwin-patches wrote:
>>>> Allow fchmodat with the AT_SYMLINK_NOFOLLOW flag to succeed on
>>>> non-symlinks. Previously it always failed, as it does on Linux. But
>>>> POSIX permits it to succeed on non-symlinks even if it fails on
>>>> The reason for following POSIX rather than Linux is to make gnulib
>>>> report that fchmodat works on Cygwin. This improves the efficiency of
>>>> packages like GNU tar that use gnulib's fchmodat module. Previously
>>>> such packages would use a gnulib replacement for fchmodat on Cygwin.
>>> Wait, what? So if Cygwin behaves like Linux, gnulib treats fchmodat
>>> as non-working? So what does gnulib do on a Linux system? Does it
>>> use its own fchmodat there, too?
>> Apparently so. Here's a comment from gnulib's test program for fchmodat:
>> /* Test whether fchmodat+AT_SYMLINK_NOFOLLOW works on non-symlinks.
>> This test fails on GNU/Linux with glibc 2.31 (but not on
>> GNU/kFreeBSD nor GNU/Hurd) and Cygwin 2.9. */
>> I agree that it's strange.
I'll go ahead and submit a revised patch for the record, and you can decide
whether you want to deviate from Linux. My own opinion is that it can't be bad
to support a flag that Linux doesn't support, but I don't feel strongly about it.
BTW, the mistake in the first version of the patch is that I forgot to specify
PC_SYM_NOFOLLOW in the path_conv constructor.
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