libc: Add O_PATH support for fgetxattr / fsetxattr

Support O_PATH file descriptors when handling fgetxattr and fsetxattr.
This avoids requiring file read access to pull extended attributes.

This is needed to support O_PATH file descriptors when calling
SELinux's fgetfilecon() call. In particular, this allows the querying
and setting of SELinux file context by using something like the following
code:

  int dirfd = open("/path/to/dir", O_DIRECTORY);
  int fd = openat(dirfd, "file", O_PATH | O_NOFOLLOW);
  char *context;
  fgetfilecon(fd, &context);

This change was motivated by a comment in
https://android-review.googlesource.com/#/c/152680/1/toys/posix/ls.c

(cherrypicked from commit 2825f10b7f61558c264231a536cf3affc0d84204)

Change-Id: Ic0cdf9f9dd0e35a63b44a4c4a08400020041eddf

0 files changed, 0 insertions, 0 deletions