Subject: [GNULIB 2/4] acl: On Linux, check for acls without libacl

From: Andreas Gruenbacher <[email-masked]>
Date: Sun, 12 Apr 2015 16:36:37 +0200

On Linux, use the getxattr syscall instead of the acl_extended_file libacl
library function to check for the presence of acls, avoiding a library
dependency.

* lib/file-has-acl.c: Include xattr headers if we have them.
(file_has_acl): On Linux, use getxattr().
* m4/acl.m4 (gl_FUNC_ACL): Define LIB_HAS_ACL as the libraries to link with for
file_has_acl(). Check for xattr headers and getxattr().
---
 lib/file-has-acl.c | 35 ++++++++++++++++++++++++++++++++++-
 m4/acl.m4          | 17 +++++++++++++++++
 modules/acl        |  2 ++
 3 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/lib/file-has-acl.c b/lib/file-has-acl.c
index de89a75..5dfe9a8 100644
--- a/lib/file-has-acl.c
+++ b/lib/file-has-acl.c
@@ -29,6 +29,13 @@
 
 #include "acl-internal.h"
 
+#if HAVE_SYS_XATTR_H
+# include <sys/xattr.h>
+#endif
+
+#if HAVE_LINUX_XATTR_H
+# include <linux/xattr.h>
+#endif
 
 /* Return 1 if NAME has a nontrivial access control list, 0 if NAME
    only has no or a base access control list, and -1 (setting errno)
@@ -41,7 +48,33 @@ file_has_acl (char const *name, struct stat const *sb)
 #if USE_ACL
   if (! S_ISLNK (sb->st_mode))
     {
-# if HAVE_ACL_GET_FILE
+
+# if HAVE_GETXATTR && defined XATTR_NAME_POSIX_ACL_ACCESS && defined XATTR_NAME_POSIX_ACL_DEFAULT
+
+      ssize_t ret;
+
+      ret = getxattr (name, XATTR_NAME_POSIX_ACL_ACCESS, NULL, 0);
+      if (ret < 0)
+	{
+	  if (errno != ENODATA)
+	    return -1;
+	}
+      else if (ret > 0)
+	return 1;
+      if (S_ISDIR (sb->st_mode))
+	{
+	  ret = getxattr (name, XATTR_NAME_POSIX_ACL_DEFAULT, NULL, 0);
+	  if (ret < 0)
+	    {
+	      if (errno != ENODATA)
+		return -1;
+	    }
+	  else if (ret > 0)
+	    return 1;
+	}
+      return 0;
+
+# elif HAVE_ACL_GET_FILE
 
       /* POSIX 1003.1e (draft 17 -- abandoned) specific version.  */
       /* Linux, FreeBSD, Mac OS X, IRIX, Tru64 */
diff --git a/m4/acl.m4 b/m4/acl.m4
index c77f0ed..a6c2a0d 100644
--- a/m4/acl.m4
+++ b/m4/acl.m4
@@ -16,6 +16,7 @@ AC_DEFUN([gl_FUNC_ACL],
 
   AC_CHECK_FUNCS_ONCE([fchmod])
   LIB_ACL=
+  LIB_HAS_ACL=
   use_acl=0
   if test "x$enable_acl" != "xno"; then
     dnl On all platforms, the ACL related API is declared in <sys/acl.h>.
@@ -124,6 +125,21 @@ int type = ACL_TYPE_EXTENDED;]])],
 
       LIBS=$ac_save_LIBS
     fi
+
+    dnl On Linux, testing if a file has an acl can be done with the getxattr
+    dnl syscall which doesn't require linking against additional libraries.
+    use_xattrs=0
+    AC_CHECK_HEADERS([sys/xattr.h linux/xattr.h])
+    if test $ac_cv_header_sys_xattr_h = yes && test $ac_cv_header_linux_xattr_h = yes; then
+      AC_CHECK_FUNCS([getxattr])
+      if test $ac_cv_func_getxattr = yes; then
+	use_xattrs=1
+      fi
+    fi
+    if test use_xattrs = 0; then
+      LIB_HAS_ACL=$LIB_ACL
+    fi
+
     if test "x$enable_acl$use_acl" = "xyes0"; then
       AC_MSG_ERROR([ACLs enabled but support not detected])
     elif test "x$enable_acl$use_acl" = "xauto0"; then
@@ -132,6 +148,7 @@ int type = ACL_TYPE_EXTENDED;]])],
     fi
   fi
   AC_SUBST([LIB_ACL])
+  AC_SUBST([LIB_HAS_ACL])
   AC_DEFINE_UNQUOTED([USE_ACL], [$use_acl],
     [Define to nonzero if you want access control list support.])
   USE_ACL=$use_acl
diff --git a/modules/acl b/modules/acl
index fdb0d72..7faec17 100644
--- a/modules/acl
+++ b/modules/acl
@@ -11,6 +11,7 @@ error
 gettext-h
 qacl
 quote
+stdbool
 
 configure.ac:
 
@@ -22,6 +23,7 @@ Include:
 
 Link:
 $(LIB_ACL)
+$(LIB_HAS_ACL)
 
 License:
 GPL
-- 
2.1.0