Re: [PATCH v2 01/11] btrfs: Add "barrier" option to support "-o remount,barrier"

[Qu Wenruo <quwenruo@cn.fujitsu.com>]

On fri, 3 Jan 2014 08:44:30 +0000, Mike Fleetwood wrote:
> On 3 January 2014 06:10, Qu Wenruo <quwenruo@cn.fujitsu.com> wrote:
>> Btrfs can be remounted without barrier, but there is no "barrier" option
>> so nobody can remount btrfs back with barrier on. Only umount and
>> mount again can re-enable barrier.(Quite awkward)
>>
>> Also the mount options in the document is also changed slightly for the
>> further pairing options changes.
>>
>> Reported-by: Daniel Blueman <daniel@quora.org>
>> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
>> Cc: David Sterba <dsterba@suse.cz>
>> ---
>> changelog:
>> v1: Add barrier option
>> v2: Change the document style to fit pairing options better
>> ---
>>   Documentation/filesystems/btrfs.txt | 13 +++++++------
>>   fs/btrfs/super.c                    |  8 +++++++-
>>   2 files changed, 14 insertions(+), 7 deletions(-)
>>
>> diff --git a/Documentation/filesystems/btrfs.txt b/Documentation/filesystems/btrfs.txt
>> index 5dd282d..2d2e016 100644
>> --- a/Documentation/filesystems/btrfs.txt
>> +++ b/Documentation/filesystems/btrfs.txt
>> @@ -38,7 +38,7 @@ Mount Options
>>   =============
>>
>>   When mounting a btrfs filesystem, the following option are accepted.
>> -Unless otherwise specified, all options default to off.
>> +Options with (*) are default options and will not show in the mount options.
>>
>>     alloc_start=<bytes>
>>          Debugging option to force all block allocations above a certain
>> @@ -138,12 +138,13 @@ Unless otherwise specified, all options default to off.
>>          Disable support for Posix Access Control Lists (ACLs).  See the
>>          acl(5) manual page for more information about ACLs.
>>
>> +  barrier(*)
>>     nobarrier
>> -        Disables the use of block layer write barriers.  Write barriers ensure
>> -       that certain IOs make it through the device cache and are on persistent
>> -       storage.  If used on a device with a volatile (non-battery-backed)
>> -       write-back cache, this option will lead to filesystem corruption on a
>> -       system crash or power loss.
>> +        Disable/enable the use of block layer write barriers.  Write barriers
> Please use
>    "Enable/Disable ..."
> to match order on the options barrier(*) then nobarrier immediately above.
>
>> +       ensure that certain IOs make it through the device cache and are on
>> +       persistent storage. If used on a device with a volatile
> And:
>    "...  If disabled on a device with a volatile"
> to make more sense when both enable and disable options are listed.
Thanks for pointing out the problem.
I'll fix it soon.

Qu
>> +       (non-battery-backed) write-back cache, this option will lead to
>> +       filesystem corruption on a system crash or power loss.
>>
>>     nodatacow
>>          Disable data copy-on-write for newly created files.  Implies nodatasum,
>> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
>> index e9c13fb..fe9d8a6 100644
>> --- a/fs/btrfs/super.c
>> +++ b/fs/btrfs/super.c
>> @@ -323,7 +323,7 @@ enum {
>>          Opt_no_space_cache, Opt_recovery, Opt_skip_balance,
>>          Opt_check_integrity, Opt_check_integrity_including_extent_data,
>>          Opt_check_integrity_print_mask, Opt_fatal_errors, Opt_rescan_uuid_tree,
>> -       Opt_commit_interval,
>> +       Opt_commit_interval, Opt_barrier,
>>          Opt_err,
>>   };
>>
>> @@ -335,6 +335,7 @@ static match_table_t tokens = {
>>          {Opt_nodatasum, "nodatasum"},
>>          {Opt_nodatacow, "nodatacow"},
>>          {Opt_nobarrier, "nobarrier"},
>> +       {Opt_barrier, "barrier"},
>>          {Opt_max_inline, "max_inline=%s"},
>>          {Opt_alloc_start, "alloc_start=%s"},
>>          {Opt_thread_pool, "thread_pool=%d"},
>> @@ -494,6 +495,11 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
>>                          btrfs_clear_opt(info->mount_opt, SSD);
>>                          btrfs_clear_opt(info->mount_opt, SSD_SPREAD);
>>                          break;
>> +               case Opt_barrier:
>> +                       if (btrfs_test_opt(root, NOBARRIER))
>> +                               btrfs_info(root->fs_info, "turning on barriers");
>> +                       btrfs_clear_opt(info->mount_opt, NOBARRIER);
>> +                       break;
>>                  case Opt_nobarrier:
>>                          btrfs_info(root->fs_info, "turning off barriers");
>>                          btrfs_set_opt(info->mount_opt, NOBARRIER);
>> --
>> 1.8.5.2
>>
> Thanks,
> Mike
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