ocfs2: Add "preferred slot" mount option

ocfs2 will attempt to assign the node the slot# provided in the mount
option. Failure to assign the preferred slot is not an error. This small
feature can be useful for automated testing.

Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

fs/ocfs2/ocfs2.h

@@ -219,6 +219,7 @@ struct ocfs2_super
 	u16 max_slots;
 	s16 node_num;
 	s16 slot_num;
+	s16 preferred_slot;
 	int s_sectsize_bits;
 	int s_clustersize;
 	int s_clustersize_bits;

fs/ocfs2/slot_map.c

@@ -121,17 +121,25 @@ static s16 __ocfs2_node_num_to_slot(struct ocfs2_slot_info *si,
 	return ret;
 }
 
-static s16 __ocfs2_find_empty_slot(struct ocfs2_slot_info *si)
+static s16 __ocfs2_find_empty_slot(struct ocfs2_slot_info *si, s16 preferred)
 {
 	int i;
 	s16 ret = OCFS2_INVALID_SLOT;
 
+	if (preferred >= 0 && preferred < si->si_num_slots) {
+		if (OCFS2_INVALID_SLOT == si->si_global_node_nums[preferred]) {
+			ret = preferred;
+			goto out;
+		}
+	}
+
 	for(i = 0; i < si->si_num_slots; i++) {
 		if (OCFS2_INVALID_SLOT == si->si_global_node_nums[i]) {
 			ret = (s16) i;
 			break;
 		}
 	}
+out:
 	return ret;
 }
 
@@ -248,7 +256,7 @@ int ocfs2_find_slot(struct ocfs2_super *osb)
 	if (slot == OCFS2_INVALID_SLOT) {
 		/* if no slot yet, then just take 1st available
 		 * one. */
-		slot = __ocfs2_find_empty_slot(si);
+		slot = __ocfs2_find_empty_slot(si, osb->preferred_slot);
 		if (slot == OCFS2_INVALID_SLOT) {
 			spin_unlock(&si->si_lock);
 			mlog(ML_ERROR, "no free slots available!\n");

fs/ocfs2/super.c

@@ -82,7 +82,8 @@ MODULE_AUTHOR("Oracle");
 MODULE_LICENSE("GPL");
 
 static int ocfs2_parse_options(struct super_block *sb, char *options,
-			       unsigned long *mount_opt, int is_remount);
+			       unsigned long *mount_opt, s16 *slot,
+			       int is_remount);
 static void ocfs2_put_super(struct super_block *sb);
 static int ocfs2_mount_volume(struct super_block *sb);
 static int ocfs2_remount(struct super_block *sb, int *flags, char *data);
@@ -140,6 +141,7 @@ enum {
 	Opt_data_ordered,
 	Opt_data_writeback,
 	Opt_atime_quantum,
+	Opt_slot,
 	Opt_err,
 };
 
@@ -154,6 +156,7 @@ static match_table_t tokens = {
 	{Opt_data_ordered, "data=ordered"},
 	{Opt_data_writeback, "data=writeback"},
 	{Opt_atime_quantum, "atime_quantum=%u"},
+	{Opt_slot, "preferred_slot=%u"},
 	{Opt_err, NULL}
 };
 
@@ -355,9 +358,10 @@ static int ocfs2_remount(struct super_block *sb, int *flags, char *data)
 	int incompat_features;
 	int ret = 0;
 	unsigned long parsed_options;
+	s16 slot;
 	struct ocfs2_super *osb = OCFS2_SB(sb);
 
-	if (!ocfs2_parse_options(sb, data, &parsed_options, 1)) {
+	if (!ocfs2_parse_options(sb, data, &parsed_options, &slot, 1)) {
 		ret = -EINVAL;
 		goto out;
 	}
@@ -534,6 +538,7 @@ static int ocfs2_fill_super(struct super_block *sb, void *data, int silent)
 	struct dentry *root;
 	int status, sector_size;
 	unsigned long parsed_opt;
+	s16 slot;
 	struct inode *inode = NULL;
 	struct ocfs2_super *osb = NULL;
 	struct buffer_head *bh = NULL;
@@ -541,7 +546,7 @@ static int ocfs2_fill_super(struct super_block *sb, void *data, int silent)
 
 	mlog_entry("%p, %p, %i", sb, data, silent);
 
-	if (!ocfs2_parse_options(sb, data, &parsed_opt, 0)) {
+	if (!ocfs2_parse_options(sb, data, &parsed_opt, &slot, 0)) {
 		status = -EINVAL;
 		goto read_super_error;
 	}
@@ -571,6 +576,7 @@ static int ocfs2_fill_super(struct super_block *sb, void *data, int silent)
 	brelse(bh);
 	bh = NULL;
 	osb->s_mount_opt = parsed_opt;
+	osb->preferred_slot = slot;
 
 	sb->s_magic = OCFS2_SUPER_MAGIC;
 
@@ -713,6 +719,7 @@ static struct file_system_type ocfs2_fs_type = {
 static int ocfs2_parse_options(struct super_block *sb,
 			       char *options,
 			       unsigned long *mount_opt,
+			       s16 *slot,
 			       int is_remount)
 {
 	int status;
@@ -722,6 +729,7 @@ static int ocfs2_parse_options(struct super_block *sb,
 		   options ? options : "(none)");
 
 	*mount_opt = 0;
+	*slot = OCFS2_INVALID_SLOT;
 
 	if (!options) {
 		status = 1;
@@ -782,6 +790,15 @@ static int ocfs2_parse_options(struct super_block *sb,
 			else
 				osb->s_atime_quantum = OCFS2_DEFAULT_ATIME_QUANTUM;
 			break;
+		case Opt_slot:
+			option = 0;
+			if (match_int(&args[0], &option)) {
+				status = 0;
+				goto bail;
+			}
+			if (option)
+				*slot = (s16)option;
+			break;
 		default:
 			mlog(ML_ERROR,
 			     "Unrecognized mount option \"%s\" "