[RFC PATCH 3/5] btrfs: Add sharedext mount option

[Goldwyn Rodrigues <rgoldwyn@suse.de>]

From: Goldwyn Rodrigues <rgoldwyn@suse.com>

The mount option to use shared pages for shared extents. If set, pass
custom file_offset_to_device function to filemap_read().

sharedext may not describe it well. Suggest a better name?

TODO Checks:
Check if the pagesize == blocksize

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
 fs/btrfs/ctree.h | 1 +
 fs/btrfs/super.c | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 4aa4f4760b72..5c97112143d6 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1415,6 +1415,7 @@ enum {
 	BTRFS_MOUNT_DISCARD_ASYNC		= (1UL << 28),
 	BTRFS_MOUNT_IGNOREBADROOTS		= (1UL << 29),
 	BTRFS_MOUNT_IGNOREDATACSUMS		= (1UL << 30),
+	BTRFS_MOUNT_SHAREDEXT			= (1UL << 31),
 };
 
 #define BTRFS_DEFAULT_COMMIT_INTERVAL	(30)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d07b18b2b250..432f40f72466 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -397,6 +397,7 @@ enum {
 #ifdef CONFIG_BTRFS_FS_REF_VERIFY
 	Opt_ref_verify,
 #endif
+	Opt_sharedext,
 	Opt_err,
 };
 
@@ -471,6 +472,7 @@ static const match_table_t tokens = {
 #ifdef CONFIG_BTRFS_FS_REF_VERIFY
 	{Opt_ref_verify, "ref_verify"},
 #endif
+	{Opt_sharedext, "sharedext"},
 	{Opt_err, NULL},
 };
 
@@ -1013,6 +1015,10 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 			btrfs_set_opt(info->mount_opt, REF_VERIFY);
 			break;
 #endif
+		case Opt_sharedext:
+			btrfs_info(info, "enabling shared memory for shared extents");
+			btrfs_set_opt(info->mount_opt, SHAREDEXT);
+			break;
 		case Opt_err:
 			btrfs_err(info, "unrecognized mount option '%s'", p);
 			ret = -EINVAL;
-- 
2.33.1