Re: [PATCH] Btrfs: allow mount -o remount,compress=no

[David Sterba]

On Wed, Apr 04, 2012 at 09:46:17PM +0200, Arnd Hannemann wrote:
> Btrfs allows to turn on compression on a mounted and used filesystem
> by issuing mount -o remount,compress=lzo.
> This patch allows to turn compression off again
> while the filesystem is mounted.

I agree it makes sense to allow for turning off the compression via
remount. Currently the mount flag FORCE_COMPRESS implies COMPRESS and
your code may lead to FORCE_COMPRESS without COMPRESS. To fix that
clear the force option as well.

For completeness, there should be also possibility of

  -o remount,compress-force=no

doing exactly the same, just a different syntax. Proposed fix below.

> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -394,15 +394,20 @@ int btrfs_parse_options(struct btrfs_root *root, char 
> *options)
>   strcmp(args[0].from, "zlib") == 0) {
>   compress_type = "zlib";
>   info->compress_type = BTRFS_COMPRESS_ZLIB;
> + btrfs_set_opt(info->mount_opt, COMPRESS);
>   } else if (strcmp(args[0].from, "lzo") == 0) {
>   compress_type = "lzo";
>   info->compress_type = BTRFS_COMPRESS_LZO;
> + btrfs_set_opt(info->mount_opt, COMPRESS);
> + } else if (strncmp(args[0].from, "no", 2) == 0) {
> + compress_type = "no";
> + info->compress_type = BTRFS_COMPRESS_NONE;
> + btrfs_clear_opt(info->mount_opt, COMPRESS);

btrfs_clear_opt(info->mount_opt, 
FORCE_COMPRESS);
compress_force = false;

>   } else {
>   ret = -EINVAL;
>   goto out;
>   }
>  
> - btrfs_set_opt(info->mount_opt, COMPRESS);
>   if (compress_force) {
>   btrfs_set_opt(info->mount_opt, FORCE_COMPRESS);
>   pr_info("btrfs: force %s compression\n",
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[PATCH] Btrfs: allow mount -o remount,compress=no

[Arnd Hannemann]

Btrfs allows to turn on compression on a mounted and used filesystem
by issuing mount -o remount,compress=lzo.
This patch allows to turn compression off again
while the filesystem is mounted.

Signed-off-by: Arnd Hannemann 
---
 fs/btrfs/super.c |7 ++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 8d5d380..f1fb6c0 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -394,15 +394,20 @@ int btrfs_parse_options(struct btrfs_root *root, char 
*options)
strcmp(args[0].from, "zlib") == 0) {
compress_type = "zlib";
info->compress_type = BTRFS_COMPRESS_ZLIB;
+   btrfs_set_opt(info->mount_opt, COMPRESS);
} else if (strcmp(args[0].from, "lzo") == 0) {
compress_type = "lzo";
info->compress_type = BTRFS_COMPRESS_LZO;
+   btrfs_set_opt(info->mount_opt, COMPRESS);
+   } else if (strncmp(args[0].from, "no", 2) == 0) {
+   compress_type = "no";
+   info->compress_type = BTRFS_COMPRESS_NONE;
+   btrfs_clear_opt(info->mount_opt, COMPRESS);
} else {
ret = -EINVAL;
goto out;
}
 
-   btrfs_set_opt(info->mount_opt, COMPRESS);
if (compress_force) {
btrfs_set_opt(info->mount_opt, FORCE_COMPRESS);
pr_info("btrfs: force %s compression\n",
-- 
1.7.9.1

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