Btrfs: Add mount option to turn off data cow

A number of workloads do not require copy on write data or checksumming.
mount -o nodatasum to disable checksums and -o nodatacow to disable
both copy on write and checksumming.

In nodatacow mode, copy on write is still performed when a given extent
is under snapshot.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 27 insertions, 7 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index ad4f280ec777..2116728d1f98 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -61,12 +61,13 @@ static void btrfs_put_super (struct super_block * sb)
 }
 
 enum {
-        Opt_subvol, Opt_nodatasum, Opt_err,
+        Opt_subvol, Opt_nodatasum, Opt_nodatacow, Opt_err,
 };
 
 static match_table_t tokens = {
         {Opt_subvol, "subvol=%s"},
         {Opt_nodatasum, "nodatasum"},
+        {Opt_nodatacow, "nodatacow"},
         {Opt_err, NULL}
 };
 
@@ -78,12 +79,20 @@ static int parse_options (char * options,
         struct btrfs_fs_info *info = NULL;
         substring_t args[MAX_OPT_ARGS];
 
-        if (root)
-                info = root->fs_info;
-
         if (!options)
                 return 1;
 
+        /*
+         * strsep changes the string, duplicate it because parse_options
+         * gets called twice
+         */
+        options = kstrdup(options, GFP_NOFS);
+        if (!options)
+                return -ENOMEM;
+
+        if (root)
+                info = root->fs_info;
+
         while ((p = strsep (&options, ",")) != NULL) {
                 int token;
                 if (!*p)
@@ -92,17 +101,28 @@ static int parse_options (char * options,
                 token = match_token(p, tokens, args);
                 switch (token) {
                 case Opt_subvol:
-                        if (subvol_name)
+                        if (subvol_name) {
                                 *subvol_name = match_strdup(&args[0]);
+                        }
                         break;
                 case Opt_nodatasum:
-                        if (root)
+                        if (info) {
+                                printk("btrfs: setting nodatacsum\n");
                                 btrfs_set_opt(info->mount_opt, NODATASUM);
+                        }
+                        break;
+                case Opt_nodatacow:
+                        if (info) {
+                                printk("btrfs: setting nodatacow\n");
+                                btrfs_set_opt(info->mount_opt, NODATACOW);
+                                btrfs_set_opt(info->mount_opt, NODATASUM);
+                        }
                         break;
                 default:
-                        return 0;
+                        break;
                 }
         }
+        kfree(options);
         return 1;
 }