"cp -p" tries to preserve GID even if preserving the UID fails.

* NEWS: Mention this new feature.
* src/copy.c (set_owner): Try to preserve just the GID,
when initial fchown/lchown fails.
* src/cp.c (re_protect): Likewise.

4 files changed, 41 insertions, 8 deletions

diff --git a/ChangeLog b/ChangeLog
index b34ad8da1..3caaaa36f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2007-11-24  Jim Meyering  <meyering@redhat.com>
+
+	"cp -p" tries to preserve GID even if preserving the UID fails.
+	* NEWS: Mention this new feature.
+	* src/copy.c (set_owner): Try to preserve just the GID,
+	when initial fchown/lchown fails.
+	* src/cp.c (re_protect): Likewise.
+
 2007-11-23  Jim Meyering  <meyering@redhat.com>
 
 	* src/runcon.c (main): Remove unused parameter, "envp".
diff --git a/NEWS b/NEWS
index 14fb3cd8b..03e16a5d1 100644
--- a/NEWS
+++ b/NEWS
@@ -29,6 +29,9 @@ GNU coreutils NEWS                                    -*- outline -*-
 
   Add SELinux support (FIXME: add details here)
 
+  cp -p tries to preserve the GID of a file even if preserving the UID
+  is not possible.
+
   uniq accepts a new option: --zero-terminated (-z).  As with the sort
   option of the same name, this makes uniq consume and produce
   NUL-terminated lines rather than newline-terminated lines.
diff --git a/src/copy.c b/src/copy.c
index 280fbf8d9..4dec5166e 100644
--- a/src/copy.c
+++ b/src/copy.c
@@ -172,7 +172,8 @@ copy_dir (char const *src_name_in, char const *dst_name_in, bool new_dst,
    safety prefer lchown if the system supports it since no
    symbolic links should be involved.  DEST_DESC must
    refer to the same file as DEST_NAME if defined.
-   Return 1 if the syscall succeeds, 0 if it fails but it's OK
+   Upon failure to set both UID and GID, try to set only the GID.
+   Return 1 if the initial syscall succeeds, 0 if it fails but it's OK
    not to preserve ownership, -1 otherwise.  */
 
 static int
@@ -183,11 +184,27 @@ set_owner (const struct cp_options *x, char const *dst_name, int dest_desc,
     {
       if (fchown (dest_desc, uid, gid) == 0)
 	return 1;
+      if (errno == EPERM || errno == EINVAL)
+        {
+	  /* We've failed to set *both*.  Now, try to set just the group
+	     ID, but ignore any failure here, and don't change errno.  */
+          int saved_errno = errno;
+          (void) fchown (dest_desc, -1, gid);
+          errno = saved_errno;
+        }
     }
   else
     {
       if (lchown (dst_name, uid, gid) == 0)
 	return 1;
+      if (errno == EPERM || errno == EINVAL)
+        {
+	  /* We've failed to set *both*.  Now, try to set just the group
+	     ID, but ignore any failure here, and don't change errno.  */
+          int saved_errno = errno;
+          (void) lchown (dst_name, -1, gid);
+          errno = saved_errno;
+        }
     }
 
   if (! chown_failure_ok (x))
diff --git a/src/cp.c b/src/cp.c
index 5859f8c1d..599498dd7 100644
--- a/src/cp.c
+++ b/src/cp.c
@@ -316,13 +316,18 @@ re_protect (char const *const_dst_name, size_t src_offset,
 
       if (x->preserve_ownership)
 	{
-	  if (lchown (dst_name, p->st.st_uid, p->st.st_gid) != 0
-	      && ! chown_failure_ok (x))
-	    {
-	      error (0, errno, _("failed to preserve ownership for %s"),
-		     quote (dst_name));
-	      return false;
-	    }
+          if (lchown (dst_name, p->st.st_uid, p->st.st_gid) != 0)
+            {
+              if (! chown_failure_ok (x))
+                {
+                  error (0, errno, _("failed to preserve ownership for %s"),
+                         quote (dst_name));
+                  return false;
+                }
+              /* Failing to preserve ownership is OK. Still, try to preserve
+                 the group, but ignore the possible error. */
+              (void) lchown (dst_name, -1, p->st.st_gid);
+            }
 	}
 
       if (x->preserve_mode)