[Bug libc/14578] fchmodat(..., AT_SYMLINK_NOFOLLOW) returns ENOTSUP on non-symlinks

["joseph at codesourcery dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14578

--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2012-09-13 17:01:22 UTC ---
glibc can't check if it's a symlink itself without a race condition.  
What does the kernel do if AT_SYMLINK_NOFOLLOW is passed to the fchmodat 
syscall (both on symlinks, and on non-symlinks?  (Any code expecting an 
lchmod syscall can clearly be removed from glibc in any case - chmod 
support for symlinks in future would have to be via a *at syscall to 
accord with current Linux kernel practice regarding adding syscalls - so 
#ifndef __NR_lchmod should be unconditional, #ifdef __NR_lchmod removed.)

If the syscall does the right thing, I suppose the check for 
AT_SYMLINK_NOFOLLOW could be moved after the code using the fchmodat 
syscall, so that the issue only applies to old kernels (for which it is 
unavoidable because of the race).

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