Linux 4.9 compat: group_info changes

In Linux 4.9, torvalds/linux@81243ea, group_info changed from 2d array via
->blocks to 1d array via ->gid. We change the spl cred functions accordingly.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closes #581

config/spl-build.m4

@@ -49,6 +49,7 @@ AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
 	SPL_AC_WAIT_ON_BIT
 	SPL_AC_MUTEX_OWNER
 	SPL_AC_INODE_LOCK
+	SPL_AC_GROUP_INFO_GID
 ])
 
 AC_DEFUN([SPL_AC_MODULE_SYMVERS], [
@@ -1574,3 +1575,25 @@ AC_DEFUN([SPL_AC_INODE_LOCK], [
 	])
 	EXTRA_KCFLAGS="$tmp_flags"
 ])
+
+dnl #
+dnl # 4.9 API change
+dnl # group_info changed from 2d array via >blocks to 1d array via ->gid
+dnl #
+AC_DEFUN([SPL_AC_GROUP_INFO_GID], [
+	AC_MSG_CHECKING([whether group_info->gid exists])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Werror"
+	SPL_LINUX_TRY_COMPILE([
+		#include <linux/cred.h>
+	],[
+		struct group_info *gi = groups_alloc(1);
+		gi->gid[0] = KGIDT_INIT(0);
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_GROUP_INFO_GID, 1, [group_info->gid exists])
+	],[
+		AC_MSG_RESULT(no)
+	])
+	EXTRA_KCFLAGS="$tmp_flags"
+])

include/sys/cred.h

@@ -34,6 +34,11 @@ typedef struct cred cred_t;
 #define	kcred		((cred_t *)(init_task.cred))
 #define	CRED()		((cred_t *)current_cred())
 
+/* Linux 4.9 API change, GROUP_AT was removed */
+#ifndef GROUP_AT
+#define	GROUP_AT(gi, i)	((gi)->gid[i])
+#endif
+
 #ifdef HAVE_KUIDGID_T
 
 #define	KUID_TO_SUID(x)		(__kuid_val(x))

module/spl/spl-cred.c

@@ -85,20 +85,26 @@ crgetngroups(const cred_t *cr)
 
 	gi = cr->group_info;
 	rc = gi->ngroups;
+#ifndef HAVE_GROUP_INFO_GID
 	/*
+	 * For Linux <= 4.8,
 	 * crgetgroups will only returns gi->blocks[0], which contains only
 	 * the first NGROUPS_PER_BLOCK groups.
 	 */
 	if (rc > NGROUPS_PER_BLOCK) {
 		WARN_ON_ONCE(1);
 		rc = NGROUPS_PER_BLOCK;
 	}
+#endif
 	return rc;
 }
 
 /*
  * Return an array of supplemental gids.  The returned address is safe
  * to use as long as the caller has taken a reference with crhold().
+ *
+ * Linux 4.9 API change, group_info changed from 2d array via ->blocks to 1d
+ * array via ->gid.
  */
 gid_t *
 crgetgroups(const cred_t *cr)
@@ -107,8 +113,12 @@ crgetgroups(const cred_t *cr)
 	gid_t *gids = NULL;
 
 	gi = cr->group_info;
+#ifdef HAVE_GROUP_INFO_GID
+	gids = KGIDP_TO_SGIDP(gi->gid);
+#else
 	if (gi->nblocks > 0)
 		gids = KGIDP_TO_SGIDP(gi->blocks[0]);
+#endif
 	return gids;
 }
 

module/splat/splat-cred.c

@@ -166,6 +166,7 @@ splat_cred_test2(struct file *file, void *arg)
         return 0;
 } /* splat_cred_test2() */
 
+#define	SPLAT_NGROUPS	32
 /*
  * Verify the groupmember() works correctly by constructing an interesting
  * CRED() and checking that the expected gids are part of it.
@@ -188,15 +189,15 @@ splat_cred_test3(struct file *file, void *arg)
 	 * 1:(NGROUPS_MAX-1).  Gid 0 is explicitly avoided so we can reliably
 	 * test for its absence in the test cases.
 	 */
-	gi = groups_alloc(NGROUPS_SMALL);
+	gi = groups_alloc(SPLAT_NGROUPS);
 	if (gi == NULL) {
 		splat_vprint(file, SPLAT_CRED_TEST3_NAME, "Failed create "
 		    "group_info for known gids: %d\n", -ENOMEM);
 		rc = -ENOMEM;
 		goto show_groups;
 	}
 
-	for (i = 0, tmp_gid = known_gid; i < NGROUPS_SMALL; i++) {
+	for (i = 0, tmp_gid = known_gid; i < SPLAT_NGROUPS; i++) {
 		splat_vprint(file, SPLAT_CRED_TEST3_NAME, "Adding gid %d "
 		    "to current CRED() (%d/%d)\n", tmp_gid, i, gi->ngroups);
 #ifdef HAVE_KUIDGID_T