Fix file-attributes race on GNU hosts

* doc/lispref/files.texi (File Attributes):
Document file-attributes atomicity.
* etc/NEWS: Document the fix.
* src/dired.c (file_attributes): New args DIRNAME and FILENAME,
for diagnostics.  All callers changed.  On platforms like
GNU/Linux that support O_PATH, fix a race condition in
file-attributes and similar functions, so that these functions do
not return nonsense if a directory entry is replaced while getting
its attributes.  On non-GNU platforms, do a better (though not
perfect) job of detecting the race, and return nil if detected.

1 files changed, 6 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index bf59749a62b..02de66b355f 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1428,6 +1428,12 @@ job of signaling list cycles instead of looping indefinitely.
 can be used for creation of temporary files of remote or mounted directories.
 
 +++
+** On GNU platforms when operating on a local file, 'file-attributes'
+no longer suffers from a race when called while another process is
+altering the filesystem.  On non-GNU platforms 'file-attributes'
+attempts to detect the race, and returns nil if it does so.
+
++++
 ** The new function 'file-local-name' can be used to specify arguments
 of remote processes.