Re: [PATCH v2] btrfs: Introduce new mount option to disable tree log replay

[Qu Wenruo]

Chandan Rajendra wrote on 2015/12/08 15:36 +0530:

On Tuesday 08 Dec 2015 14:10:33 Qu Wenruo wrote:

Introduce a new mount option "nologreplay" to co-operate with "ro" mount
option to get real readonly mount, like "norecovery" in ext* and xfs.

Since the new parse_options() need to check new flags at remount time,
so add a new parameter for parse_options().

Signed-off-by: Qu Wenruo 
---
v2:
   Make RO check mandatory for btrfs_parse_options().
   Add btrfs_show_options() support for nologreplay.

   Document for btrfs-mount(5) will follow after the patch being merged.
---
  Documentation/filesystems/btrfs.txt |  7 +++
  fs/btrfs/ctree.h|  4 +++-
  fs/btrfs/disk-io.c  |  7 ---
  fs/btrfs/super.c| 29 +
  4 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/Documentation/filesystems/btrfs.txt
b/Documentation/filesystems/btrfs.txt index c772b47..7ad5b93 100644
--- a/Documentation/filesystems/btrfs.txt
+++ b/Documentation/filesystems/btrfs.txt
@@ -168,6 +168,13 @@ Options with (*) are default options and will not show
in the mount options. notreelog
Enable/disable the tree logging used for fsync and O_SYNC writes.

+  nologreplay
+   Disable the log tree replay at mount time to prevent devices get
+   modified. Must be use with 'ro' mount option.
+   A filesystem mounted with the 'nologreplay' option cannot
+   transition to a read-write mount via remount,rw - the filesystem
+   must be unmounted and remounted if read-write access is desired.
+


May be the following is slightly better ...

Disable the log tree replay at mount time to prevent filesystem from getting
modified. Must be used with 'ro' mount option.  A filesystem mounted with the
'nologreplay' option cannot transition to a read-write mount via remount,rw -
the filesystem must be unmounted and mounted back again if read-write access
is desired.


Thanks for the review and advice.

Since I'm not a native English speaker, I'll follow your advice.
(Yeah, remount in my patch is confusing.)

I'll update it to v3 with Document update only

Thank,
Qu


Aside from above, everything else looks good to me.

Reviewed-by: Chandan Rajendra 




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Re: [PATCH v2] btrfs: Introduce new mount option to disable tree log replay

[Chandan Rajendra]

On Tuesday 08 Dec 2015 14:10:33 Qu Wenruo wrote:
> Introduce a new mount option "nologreplay" to co-operate with "ro" mount
> option to get real readonly mount, like "norecovery" in ext* and xfs.
> 
> Since the new parse_options() need to check new flags at remount time,
> so add a new parameter for parse_options().
> 
> Signed-off-by: Qu Wenruo 
> ---
> v2:
>   Make RO check mandatory for btrfs_parse_options().
>   Add btrfs_show_options() support for nologreplay.
> 
>   Document for btrfs-mount(5) will follow after the patch being merged.
> ---
>  Documentation/filesystems/btrfs.txt |  7 +++
>  fs/btrfs/ctree.h|  4 +++-
>  fs/btrfs/disk-io.c  |  7 ---
>  fs/btrfs/super.c| 29 +
>  4 files changed, 39 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/filesystems/btrfs.txt
> b/Documentation/filesystems/btrfs.txt index c772b47..7ad5b93 100644
> --- a/Documentation/filesystems/btrfs.txt
> +++ b/Documentation/filesystems/btrfs.txt
> @@ -168,6 +168,13 @@ Options with (*) are default options and will not show
> in the mount options. notreelog
>   Enable/disable the tree logging used for fsync and O_SYNC writes.
> 
> +  nologreplay
> + Disable the log tree replay at mount time to prevent devices get
> + modified. Must be use with 'ro' mount option.
> + A filesystem mounted with the 'nologreplay' option cannot
> + transition to a read-write mount via remount,rw - the filesystem
> + must be unmounted and remounted if read-write access is desired.
> +

May be the following is slightly better ...

Disable the log tree replay at mount time to prevent filesystem from getting
modified. Must be used with 'ro' mount option.  A filesystem mounted with the
'nologreplay' option cannot transition to a read-write mount via remount,rw -
the filesystem must be unmounted and mounted back again if read-write access
is desired.

Aside from above, everything else looks good to me.

Reviewed-by: Chandan Rajendra 

-- 
chandan

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Re: [PATCH v2] btrfs: Introduce new mount option to disable tree log replay

[Austin S Hemmelgarn]

On 2015-12-08 01:10, Qu Wenruo wrote:

Introduce a new mount option "nologreplay" to co-operate with "ro" mount
option to get real readonly mount, like "norecovery" in ext* and xfs.

Since the new parse_options() need to check new flags at remount time,
so add a new parameter for parse_options().

Signed-off-by: Qu Wenruo 
---
v2:
   Make RO check mandatory for btrfs_parse_options().
   Add btrfs_show_options() support for nologreplay.

   Document for btrfs-mount(5) will follow after the patch being merged.


Same set of tests I ran against the last version, still no issues, so:
Tested-by: Austin S. Hemmelgarn




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Re: [PATCH v2] btrfs: Introduce new mount option to disable tree log replay

[Qu Wenruo]

Roman Mamedov wrote on 2015/12/08 11:31 +0500:

On Tue,  8 Dec 2015 14:10:33 +0800
Qu Wenruo  wrote:


Introduce a new mount option "nologreplay" to co-operate with "ro" mount
option to get real readonly mount, like "norecovery" in ext* and xfs.


Maybe name it "norecovery" too, for simplicity and consistency?


That's also our first idea.
But the sad fact is, btrfs already has a mount option called "recovery".

So "norecovery" here will just be considered as a mount option to 
disable "recovery", and that will make things more confusing.


And finally we choose the name "nologreplay".

Thanks,
Qu



The actual effect of "norecovery" in ext* and xfs is to also disable log
replay, but that's an under-the-hood detail not relevant to the user.

---
Mount options for ext3

norecovery/noload
   Don't load the journal on mounting.  Note that if the filesystem
   was not unmounted cleanly, skipping the journal replay will lead
   to  the  filesystem  containing inconsistencies that can lead to
   any number of problems.
---
Mount options for xfs

norecovery
   The filesystem will be mounted without running log recovery.  If
   the filesystem was not cleanly unmounted, it  is  likely  to  be
   inconsistent  when  mounted  in  norecovery mode.  Some files or
   directories may not be accessible because of this.   Filesystems
   mounted  norecovery  must be mounted read-only or the mount will
   fail.
---




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Re: [PATCH v2] btrfs: Introduce new mount option to disable tree log replay

[Roman Mamedov]

On Tue,  8 Dec 2015 14:10:33 +0800
Qu Wenruo  wrote:

> Introduce a new mount option "nologreplay" to co-operate with "ro" mount
> option to get real readonly mount, like "norecovery" in ext* and xfs.

Maybe name it "norecovery" too, for simplicity and consistency?

The actual effect of "norecovery" in ext* and xfs is to also disable log
replay, but that's an under-the-hood detail not relevant to the user.

---
Mount options for ext3

   norecovery/noload
  Don't load the journal on mounting.  Note that if the filesystem
  was not unmounted cleanly, skipping the journal replay will lead
  to  the  filesystem  containing inconsistencies that can lead to
  any number of problems.
---
Mount options for xfs

   norecovery
  The filesystem will be mounted without running log recovery.  If
  the filesystem was not cleanly unmounted, it  is  likely  to  be
  inconsistent  when  mounted  in  norecovery mode.  Some files or
  directories may not be accessible because of this.   Filesystems
  mounted  norecovery  must be mounted read-only or the mount will
  fail.
---

-- 
With respect,
Roman


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