mempolicy: support optional mode flags

With the evolution of mempolicies, it is necessary to support mempolicy mode
flags that specify how the policy shall behave in certain circumstances.  The
most immediate need for mode flag support is to suppress remapping the
nodemask of a policy at the time of rebind.

Both the mempolicy mode and flags are passed by the user in the 'int policy'
formal of either the set_mempolicy() or mbind() syscall.  A new constant,
MPOL_MODE_FLAGS, represents the union of legal optional flags that may be
passed as part of this int.  Mempolicies that include illegal flags as part of
their policy are rejected as invalid.

An additional member to struct mempolicy is added to support the mode flags:

	struct mempolicy {
		...
		unsigned short policy;
		unsigned short flags;
	}

The splitting of the 'int' actual passed by the user is done in
sys_set_mempolicy() and sys_mbind() for their respective syscalls.  This is
done by intersecting the actual with MPOL_MODE_FLAGS, rejecting the syscall of
there are additional flags, and storing it in the new 'flags' member of struct
mempolicy.  The intersection of the actual with ~MPOL_MODE_FLAGS is stored in
the 'policy' member of the struct and all current users of pol->policy remain
unchanged.

The union of the policy mode and optional mode flags is passed back to the
user in get_mempolicy().

This combination of mode and flags within the same actual does not break
userspace code that relies on get_mempolicy(&policy, ...) and either

	switch (policy) {
	case MPOL_BIND:
		...
	case MPOL_INTERLEAVE:
		...
	};

statements or

	if (policy == MPOL_INTERLEAVE) {
		...
	}

statements.  Such applications would need to use optional mode flags when
calling set_mempolicy() or mbind() for these previously implemented statements
to stop working.  If an application does start using optional mode flags, it
will need to mask the optional flags off the policy in switch and conditional
statements that only test mode.

An additional member is also added to struct shmem_sb_info to store the
optional mode flags.

[hugh@veritas.com: shmem mpol: fix build warning]
Cc: Paul Jackson <pj@sgi.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 8 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index d8ef7ba831a..1ccf794fbe6 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1080,9 +1080,10 @@ redirty:
 #ifdef CONFIG_NUMA
 #ifdef CONFIG_TMPFS
 static int shmem_parse_mpol(char *value, unsigned short *policy,
-			    nodemask_t *policy_nodes)
+			unsigned short *mode_flags, nodemask_t *policy_nodes)
 {
 	char *nodelist = strchr(value, ':');
+	char *flags = strchr(value, '=');
 	int err = 1;
 
 	if (nodelist) {
@@ -1093,6 +1094,8 @@ static int shmem_parse_mpol(char *value, unsigned short *policy,
 		if (!nodes_subset(*policy_nodes, node_states[N_HIGH_MEMORY]))
 			goto out;
 	}
+	if (flags)
+		*flags++ = '\0';
 	if (!strcmp(value, "default")) {
 		*policy = MPOL_DEFAULT;
 		/* Don't allow a nodelist */
@@ -1122,6 +1125,8 @@ static int shmem_parse_mpol(char *value, unsigned short *policy,
 			*policy_nodes = node_states[N_HIGH_MEMORY];
 		err = 0;
 	}
+	if (flags) {
+	}
 out:
 	/* Restore string for error message */
 	if (nodelist)
@@ -1130,7 +1135,7 @@ out:
 }
 
 static void shmem_show_mpol(struct seq_file *seq, unsigned short policy,
-			    const nodemask_t policy_nodes)
+			unsigned short flags, const nodemask_t policy_nodes)
 {
 	char *policy_string;
 
@@ -1199,13 +1204,13 @@ static struct page *shmem_alloc_page(gfp_t gfp,
 #else /* !CONFIG_NUMA */
 #ifdef CONFIG_TMPFS
 static inline int shmem_parse_mpol(char *value, unsigned short *policy,
-						nodemask_t *policy_nodes)
+			unsigned short *mode_flags, nodemask_t *policy_nodes)
 {
 	return 1;
 }
 
 static inline void shmem_show_mpol(struct seq_file *seq, unsigned short policy,
-			    const nodemask_t policy_nodes)
+			unsigned short flags, const nodemask_t policy_nodes)
 {
 }
 #endif /* CONFIG_TMPFS */
@@ -1578,7 +1583,7 @@ shmem_get_inode(struct super_block *sb, int mode, dev_t dev)
 			inode->i_op = &shmem_inode_operations;
 			inode->i_fop = &shmem_file_operations;
 			mpol_shared_policy_init(&info->policy, sbinfo->policy,
-							&sbinfo->policy_nodes);
+					sbinfo->flags, &sbinfo->policy_nodes);
 			break;
 		case S_IFDIR:
 			inc_nlink(inode);
@@ -1592,7 +1597,7 @@ shmem_get_inode(struct super_block *sb, int mode, dev_t dev)
 			 * Must not load anything in the rbtree,
 			 * mpol_free_shared_policy will not be called.
 			 */
-			mpol_shared_policy_init(&info->policy, MPOL_DEFAULT,
+			mpol_shared_policy_init(&info->policy, MPOL_DEFAULT, 0,
 						NULL);
 			break;
 		}
@@ -2209,7 +2214,7 @@ static int shmem_parse_options(char *options, struct shmem_sb_info *sbinfo,
 				goto bad_val;
 		} else if (!strcmp(this_char,"mpol")) {
 			if (shmem_parse_mpol(value, &sbinfo->policy,
-					     &sbinfo->policy_nodes))
+				&sbinfo->flags, &sbinfo->policy_nodes))
 				goto bad_val;
 		} else {
 			printk(KERN_ERR "tmpfs: Bad mount option %s\n",
@@ -2261,6 +2266,7 @@ static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
 	sbinfo->max_inodes  = config.max_inodes;
 	sbinfo->free_inodes = config.max_inodes - inodes;
 	sbinfo->policy      = config.policy;
+	sbinfo->flags	    = config.flags;
 	sbinfo->policy_nodes = config.policy_nodes;
 out:
 	spin_unlock(&sbinfo->stat_lock);
@@ -2282,7 +2288,8 @@ static int shmem_show_options(struct seq_file *seq, struct vfsmount *vfs)
 		seq_printf(seq, ",uid=%u", sbinfo->uid);
 	if (sbinfo->gid != 0)
 		seq_printf(seq, ",gid=%u", sbinfo->gid);
-	shmem_show_mpol(seq, sbinfo->policy, sbinfo->policy_nodes);
+	shmem_show_mpol(seq, sbinfo->policy, sbinfo->flags,
+			sbinfo->policy_nodes);
 	return 0;
 }
 #endif /* CONFIG_TMPFS */
@@ -2313,6 +2320,7 @@ static int shmem_fill_super(struct super_block *sb,
 	sbinfo->uid = current->fsuid;
 	sbinfo->gid = current->fsgid;
 	sbinfo->policy = MPOL_DEFAULT;
+	sbinfo->flags = 0;
 	sbinfo->policy_nodes = node_states[N_HIGH_MEMORY];
 	sb->s_fs_info = sbinfo;