Work better if stat etc. are interrupted

Quit or retry if fstat, lstat, stat or openat fail with EINTR.
This should fix some bugs on platforms where accessing files via
NFS can fail that way (Bug#9256).
* src/dired.c (file_attributes):
* src/fileio.c (file_directory_p) [O_PATH]:
Use emacs_openat instead of openat.
* src/dired.c (file_attributes): Use emacs_fstatat instead of fstatat.
* src/fileio.c (barf_or_query_if_file_exists, Frename_file):
* src/filelock.c (rename_lock_file):
Use emacs_fstatat instead of lstat.
* src/fileio.c (file_directory_p, Ffile_regular_p, Ffile_modes)
(Ffile_newer_than_file_p, Fverify_visited_file_modtime)
(Fset_visited_file_modtime, auto_save_1):
* src/lread.c (Fload):
* src/sysdep.c (get_current_dir_name_or_unreachable):
Use emacs_fstatat instead of stat.
* src/sysdep.c (emacs_fstatat, emacs_openat): New functions.
(emacs_open): Redo in terms of emacs_open.

6 files changed, 63 insertions, 25 deletions

diff --git a/src/dired.c b/src/dired.c
index 611477aa4ef..f013a4cea03 100644
--- a/src/dired.c
+++ b/src/dired.c
@@ -937,7 +937,7 @@ file_attributes (int fd, char const *name,
   int err = EINVAL;
 
 #if defined O_PATH && !defined HAVE_CYGWIN_O_PATH_BUG
-  int namefd = openat (fd, name, O_PATH | O_CLOEXEC | O_NOFOLLOW);
+  int namefd = emacs_openat (fd, name, O_PATH | O_CLOEXEC | O_NOFOLLOW, 0);
   if (namefd < 0)
     err = errno;
   else
@@ -970,7 +970,7 @@ file_attributes (int fd, char const *name,
          information to be accurate.  */
       w32_stat_get_owner_group = 1;
 #endif
-      err = fstatat (fd, name, &s, AT_SYMLINK_NOFOLLOW) == 0 ? 0 : errno;
+      err = emacs_fstatat (fd, name, &s, AT_SYMLINK_NOFOLLOW) == 0 ? 0 : errno;
 #ifdef WINDOWSNT
       w32_stat_get_owner_group = 0;
 #endif
diff --git a/src/fileio.c b/src/fileio.c
index 34934dd6df6..87a17eab425 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -1952,7 +1952,10 @@ barf_or_query_if_file_exists (Lisp_Object absname, bool known_to_exist,
 
   encoded_filename = ENCODE_FILE (absname);
 
-  if (! known_to_exist && lstat (SSDATA (encoded_filename), &statbuf) == 0)
+  if (! known_to_exist
+      && (emacs_fstatat (AT_FDCWD, SSDATA (encoded_filename),
+                         &statbuf, AT_SYMLINK_NOFOLLOW)
+          == 0))
     {
       if (S_ISDIR (statbuf.st_mode))
         xsignal2 (Qfile_error,
@@ -2555,7 +2558,9 @@ This is what happens in interactive use with M-x.  */)
   bool dirp = !NILP (Fdirectory_name_p (file));
   if (!dirp)
     {
-      if (lstat (SSDATA (encoded_file), &file_st) != 0)
+      if (emacs_fstatat (AT_FDCWD, SSDATA (encoded_file),
+                         &file_st, AT_SYMLINK_NOFOLLOW)
+          != 0)
         report_file_error ("Renaming", list2 (file, newname));
       dirp = S_ISDIR (file_st.st_mode) != 0;
     }
@@ -2928,7 +2933,8 @@ file_directory_p (Lisp_Object file)
 #else
 # ifdef O_PATH
   /* Use O_PATH if available, as it avoids races and EOVERFLOW issues.  */
-  int fd = openat (AT_FDCWD, SSDATA (file), O_PATH | O_CLOEXEC | O_DIRECTORY);
+  int fd = emacs_openat (AT_FDCWD, SSDATA (file),
+                         O_PATH | O_CLOEXEC | O_DIRECTORY, 0);
   if (0 <= fd)
     {
       emacs_close (fd);
@@ -2939,9 +2945,9 @@ file_directory_p (Lisp_Object file)
   /* O_PATH is defined but evidently this Linux kernel predates 2.6.39.
      Fall back on generic POSIX code.  */
 # endif
-  /* Use file_accessible_directory_p, as it avoids stat EOVERFLOW
+  /* Use file_accessible_directory_p, as it avoids fstatat EOVERFLOW
      problems and could be cheaper.  However, if it fails because FILE
-     is inaccessible, fall back on stat; if the latter fails with
+     is inaccessible, fall back on fstatat; if the latter fails with
      EOVERFLOW then FILE must have been a directory unless a race
      condition occurred (a problem hard to work around portably).  */
   if (file_accessible_directory_p (file))
@@ -2949,7 +2955,7 @@ file_directory_p (Lisp_Object file)
   if (errno != EACCES)
     return false;
   struct stat st;
-  if (stat (SSDATA (file), &st) != 0)
+  if (emacs_fstatat (AT_FDCWD, SSDATA (file), &st, 0) != 0)
     return errno == EOVERFLOW;
   if (S_ISDIR (st.st_mode))
     return true;
@@ -3080,7 +3086,7 @@ See `file-symlink-p' to distinguish symlinks.  */)
   Vw32_get_true_file_attributes = Qt;
 #endif
 
-  int stat_result = stat (SSDATA (absname), &st);
+  int stat_result = emacs_fstatat (AT_FDCWD, SSDATA (absname), &st, 0);
 
 #ifdef WINDOWSNT
   Vw32_get_true_file_attributes = true_attributes;
@@ -3340,7 +3346,7 @@ Return nil if FILENAME does not exist.  */)
   if (!NILP (handler))
     return call2 (handler, Qfile_modes, absname);
 
-  if (stat (SSDATA (ENCODE_FILE (absname)), &st) != 0)
+  if (emacs_fstatat (AT_FDCWD, SSDATA (ENCODE_FILE (absname)), &st, 0) != 0)
     return file_attribute_errno (absname, errno);
   return make_fixnum (st.st_mode & 07777);
 }
@@ -3486,7 +3492,7 @@ otherwise, if FILE2 does not exist, the answer is t.  */)
     return call3 (handler, Qfile_newer_than_file_p, absname1, absname2);
 
   int err1;
-  if (stat (SSDATA (ENCODE_FILE (absname1)), &st1) == 0)
+  if (emacs_fstatat (AT_FDCWD, SSDATA (ENCODE_FILE (absname1)), &st1, 0) == 0)
     err1 = 0;
   else
     {
@@ -3494,7 +3500,7 @@ otherwise, if FILE2 does not exist, the answer is t.  */)
       if (err1 != EOVERFLOW)
         return file_attribute_errno (absname1, err1);
     }
-  if (stat (SSDATA (ENCODE_FILE (absname2)), &st2) != 0)
+  if (emacs_fstatat (AT_FDCWD, SSDATA (ENCODE_FILE (absname2)), &st2, 0) != 0)
     {
       file_attribute_errno (absname2, errno);
       return Qt;
@@ -3880,7 +3886,7 @@ by calling `format-decode', which see.  */)
           if (end_offset < 0)
             buffer_overflow ();
 
-          /* The file size returned from stat may be zero, but data
+          /* The file size returned from fstat may be zero, but data
              may be readable nonetheless, for example when this is a
              file in the /proc filesystem.  */
           if (end_offset == 0)
@@ -5625,7 +5631,7 @@ See Info node `(elisp)Modification Time' for more details.  */)
 
   filename = ENCODE_FILE (BVAR (b, filename));
 
-  mtime = (stat (SSDATA (filename), &st) == 0
+  mtime = (emacs_fstatat (AT_FDCWD, SSDATA (filename), &st, 0) == 0
            ? get_stat_mtime (&st)
            : time_error_value (errno));
   if (timespec_cmp (mtime, b->modtime) == 0
@@ -5689,7 +5695,8 @@ in `current-time' or an integer flag as returned by `visited-file-modtime'.  */)
         /* The handler can find the file name the same way we did.  */
         return call2 (handler, Qset_visited_file_modtime, Qnil);
 
-      if (stat (SSDATA (ENCODE_FILE (filename)), &st) == 0)
+      if (emacs_fstatat (AT_FDCWD, SSDATA (ENCODE_FILE (filename)), &st, 0)
+          == 0)
         {
           current_buffer->modtime = get_stat_mtime (&st);
           current_buffer->modtime_size = st.st_size;
@@ -5728,12 +5735,14 @@ auto_save_1 (void)
   /* Get visited file's mode to become the auto save file's mode.  */
   if (! NILP (BVAR (current_buffer, filename)))
     {
-      if (stat (SSDATA (BVAR (current_buffer, filename)), &st) >= 0)
+      if (emacs_fstatat (AT_FDCWD, SSDATA (BVAR (current_buffer, filename)),
+                         &st, 0)
+          == 0)
         /* But make sure we can overwrite it later!  */
         auto_save_mode_bits = (st.st_mode | 0600) & 0777;
       else if (modes = Ffile_modes (BVAR (current_buffer, filename)),
                FIXNUMP (modes))
-        /* Remote files don't cooperate with stat.  */
+        /* Remote files don't cooperate with fstatat.  */
         auto_save_mode_bits = (XFIXNUM (modes) | 0600) & 0777;
     }
 
diff --git a/src/filelock.c b/src/filelock.c
index b28f16e9b5a..73202f0b2c4 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -347,7 +347,8 @@ rename_lock_file (char const *old, char const *new, bool force)
          potential race condition since some other process may create
          NEW immediately after the existence check, but it's the best
          we can portably do here.  */
-      if (lstat (new, &st) == 0 || errno == EOVERFLOW)
+      if (emacs_fstatat (AT_FDCWD, new, &st, AT_SYMLINK_NOFOLLOW) == 0
+          || errno == EOVERFLOW)
         {
           errno = EEXIST;
           return -1;
diff --git a/src/lisp.h b/src/lisp.h
index 4bcd1228443..0bd375658e2 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4605,6 +4605,8 @@ extern void seed_random (void *, ptrdiff_t);
 extern void init_random (void);
 extern void emacs_backtrace (int);
 extern AVOID emacs_abort (void) NO_INLINE;
+extern int emacs_fstatat (int, char const *, void *, int);
+extern int emacs_openat (int, char const *, int, int);
 extern int emacs_open (const char *, int, int);
 extern int emacs_pipe (int[2]);
 extern int emacs_close (int);
diff --git a/src/lread.c b/src/lread.c
index 4e9860d5dc8..69dd73912bc 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -1353,11 +1353,11 @@ Return t if the file exists and loads successfully.  */)
              ignores suffix order due to load_prefer_newer.  */
           if (!load_prefer_newer && is_elc)
             {
-              result = stat (SSDATA (efound), &s1);
+              result = emacs_fstatat (AT_FDCWD, SSDATA (efound), &s1, 0);
               if (result == 0)
                 {
                   SSET (efound, SBYTES (efound) - 1, 0);
-                  result = stat (SSDATA (efound), &s2);
+                  result = emacs_fstatat (AT_FDCWD, SSDATA (efound), &s2, 0);
                   SSET (efound, SBYTES (efound) - 1, 'c');
                 }
 
diff --git a/src/sysdep.c b/src/sysdep.c
index c6344d8cec7..e8e8bbfb502 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -312,8 +312,8 @@ get_current_dir_name_or_unreachable (void)
   if (pwd
       && (pwdlen = strnlen (pwd, bufsize_max)) < bufsize_max
       && IS_DIRECTORY_SEP (pwd[pwdlen && IS_DEVICE_SEP (pwd[1]) ? 2 : 0])
-      && stat (pwd, &pwdstat) == 0
-      && stat (".", &dotstat) == 0
+      && emacs_fstatat (AT_FDCWD, pwd, &pwdstat, 0) == 0
+      && emacs_fstatat (AT_FDCWD, ".", &dotstat, 0) == 0
       && dotstat.st_ino == pwdstat.st_ino
       && dotstat.st_dev == pwdstat.st_dev)
     {
@@ -2449,7 +2449,27 @@ emacs_abort (void)
 }
 #endif
 
-/* Open FILE for Emacs use, using open flags OFLAG and mode MODE.
+/* Assuming the directory DIRFD, store information about FILENAME into *ST,
+   using FLAGS to control how the status is obtained.
+   Do not fail merely because fetching info was interrupted by a signal.
+   Allow the user to quit.
+
+   The type of ST is void * instead of struct stat * because the
+   latter type would be problematic in lisp.h.  Some platforms may
+   play tricks like "#define stat stat64" in <sys/stat.h>, and lisp.h
+   does not include <sys/stat.h>.  */
+
+int
+emacs_fstatat (int dirfd, char const *filename, void *st, int flags)
+{
+  int r;
+  while ((r = fstatat (dirfd, filename, st, flags)) != 0 && errno == EINTR)
+    maybe_quit ();
+  return r;
+}
+
+/* Assuming the directory DIRFD, open FILE for Emacs use,
+   using open flags OFLAGS and mode MODE.
    Use binary I/O on systems that care about text vs binary I/O.
    Arrange for subprograms to not inherit the file descriptor.
    Prefer a method that is multithread-safe, if available.
@@ -2457,17 +2477,23 @@ emacs_abort (void)
    Allow the user to quit.  */
 
 int
-emacs_open (const char *file, int oflags, int mode)
+emacs_openat (int dirfd, char const *file, int oflags, int mode)
 {
   int fd;
   if (! (oflags & O_TEXT))
     oflags |= O_BINARY;
   oflags |= O_CLOEXEC;
-  while ((fd = open (file, oflags, mode)) < 0 && errno == EINTR)
+  while ((fd = openat (dirfd, file, oflags, mode)) < 0 && errno == EINTR)
     maybe_quit ();
   return fd;
 }
 
+int
+emacs_open (char const *file, int oflags, int mode)
+{
+  return emacs_openat (AT_FDCWD, file, oflags, mode);
+}
+
 /* Open FILE as a stream for Emacs use, with mode MODE.
    Act like emacs_open with respect to threads, signals, and quits.  */