Re: touch and utimens troubles on new/old software combinations

[Eric Blake]

Andreas Schwab <schwab <at> suse.de> writes:

> 
> Mike Frysinger <vapier <at> gentoo.org> writes:
> 
> > also after reading it, i dont think gnu/stubs.h would help in this 
particular 
> > case.  gnulib would need a runtime test to detect that utimensat() is 
> > actually not available.
> 
> That should be pretty easy, just fall through to the fallback code when
> errno == ENOSYS.
> 
> Andreas.
> 

Does this solve your problem?  Unfortunately, it bloats code in the case where 
utimensat works just fine in the kernel.

>From b566edc2489a889d97416d2390be7796aa8cdbeb Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Mon, 2 Jun 2008 15:08:14 -0600
Subject: [PATCH] Provide futimens/utimensat fallbacks for older kernels.

* lib/utimens.c (gl_futimens) [HAVE_UTIMENSAT, HAVE_FUTIMENS]:
Provide runtime fallback if kernel lacks support.
Reported by Mike Frysinger.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog     |    7 +++++++
 lib/utimens.c |   43 ++++++++++++++++++++++++++-----------------
 2 files changed, 33 insertions(+), 17 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 84346f7..c552fd5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2008-06-02  Eric Blake  <address@hidden>
+
+       Provide fallback for older kernels.
+       * lib/utimens.c (gl_futimens) [HAVE_UTIMENSAT, HAVE_FUTIMENS]:
+       Provide runtime fallback if kernel lacks support.
+       Reported by Mike Frysinger.
+
 2008-06-01  Bruno Haible  <address@hidden>
 
        * lib/copy-acl.c (qcopy_acl): New function, extracted from copy_acl.
diff --git a/lib/utimens.c b/lib/utimens.c
index 25bc965..134310b 100644
--- a/lib/utimens.c
+++ b/lib/utimens.c
@@ -96,20 +96,30 @@ gl_futimens (int fd ATTRIBUTE_UNUSED,
 #endif
 
   /* POSIX 200x added two interfaces to set file timestamps with
-     nanosecond resolution.  */
+     nanosecond resolution.  We provide a fallback for ENOSYS (for
+     example, compiling against Linux 2.6.25 kernel headers and glibc
+     2.7, but running on Linux 2.6.18 kernel).  */
 #if HAVE_UTIMENSAT
   if (fd < 0)
-    return utimensat (AT_FDCWD, file, timespec, 0);
+    {
+      int result = utimensat (AT_FDCWD, file, timespec, 0);
+      if (result == 0 || errno != ENOSYS)
+        return result;
+    }
 #endif
 #if HAVE_FUTIMENS
-  return futimens (fd, timespec);
-#else
+  {
+    int result = futimens (fd, timespec);
+    if (result == 0 || errno != ENOSYS)
+      return result;
+  }
+#endif
 
   /* The platform lacks an interface to set file timestamps with
      nanosecond resolution, so do the best we can, discarding any
      fractional part of the timestamp.  */
   {
-# if HAVE_FUTIMESAT || HAVE_WORKING_UTIMES
+#if HAVE_FUTIMESAT || HAVE_WORKING_UTIMES
     struct timeval timeval[2];
     struct timeval const *t;
     if (timespec)
@@ -125,9 +135,9 @@ gl_futimens (int fd ATTRIBUTE_UNUSED,
 
     if (fd < 0)
       {
-#  if HAVE_FUTIMESAT
+# if HAVE_FUTIMESAT
        return futimesat (AT_FDCWD, file, t);
-#  endif
+# endif
       }
     else
       {
@@ -141,21 +151,21 @@ gl_futimens (int fd ATTRIBUTE_UNUSED,
           worth optimizing, and who knows what other messed-up systems
           are out there?  So play it safe and fall back on the code
           below.  */
-#  if HAVE_FUTIMESAT
+# if HAVE_FUTIMESAT
        if (futimesat (fd, NULL, t) == 0)
          return 0;
-#  elif HAVE_FUTIMES
+# elif HAVE_FUTIMES
        if (futimes (fd, t) == 0)
          return 0;
-#  endif
+# endif
       }
-# endif /* HAVE_FUTIMESAT || HAVE_WORKING_UTIMES */
+#endif /* HAVE_FUTIMESAT || HAVE_WORKING_UTIMES */
 
     if (!file)
       {
-# if ! (HAVE_FUTIMESAT || (HAVE_WORKING_UTIMES && HAVE_FUTIMES))
+#if ! (HAVE_FUTIMESAT || (HAVE_WORKING_UTIMES && HAVE_FUTIMES))
        errno = ENOSYS;
-# endif
+#endif
 
        /* Prefer EBADF to ENOSYS if both error numbers apply.  */
        if (errno == ENOSYS)
@@ -170,9 +180,9 @@ gl_futimens (int fd ATTRIBUTE_UNUSED,
        return -1;
       }
 
-# if HAVE_WORKING_UTIMES
+#if HAVE_WORKING_UTIMES
     return utimes (file, t);
-# else
+#else
     {
       struct utimbuf utimbuf;
       struct utimbuf const *ut;
@@ -187,9 +197,8 @@ gl_futimens (int fd ATTRIBUTE_UNUSED,
 
       return utime (file, ut);
     }
-# endif /* !HAVE_WORKING_UTIMES */
+#endif /* !HAVE_WORKING_UTIMES */
   }
-#endif /* !HAVE_FUTIMENS */
 }
 
 /* Set the access and modification time stamps of FILE to be
-- 
1.5.5.1