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Date:   Thu, 3 Oct 2019 09:55:34 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Благодаренко Артём 
        <artem.blagodarenko@...il.com>
Cc:     linux-ext4 <linux-ext4@...r.kernel.org>, adilger.kernel@...ger.ca
Subject: Re: [PATCH] ext2fs: add ext2fs_read_sb that returns superblock

We just discussed this on the ext4 developer concall today, and Ted is looking into it. 

Cheers, Andreas

> On Oct 3, 2019, at 09:47, Благодаренко Артём <artem.blagodarenko@...il.com> wrote:
> 
> Hello,
> 
> Does anybody wants to give any feedback for this?
> e2label became really faster on large partitions with this patch. Probably it can be useful.
> 
> Ted, what do you think?
> 
> Thanks,
> Artem Blagodarenko.
> 
> 
> 
>> On 5 Sep 2019, at 14:01, Artem Blagodarenko <artem.blagodarenko@...il.com> wrote:
>> 
>> tune2fs is used to make e2label duties.  ext2fs_open2() reads group
>> descriptors which are not used during disk label obtaining, but takes
>> a lot of time on large partitions.
>> 
>> This patch adds ext2fs_read_sb(), there only initialized superblock
>> is returned This saves time dramatically.
>> 
>> Signed-off-by: Artem Blagodarenko <c17828@...y.com>
>> Cray-bug-id: LUS-5777
>> ---
>> lib/ext2fs/ext2fs.h |  2 ++
>> lib/ext2fs/openfs.c | 16 ++++++++++++++++
>> misc/tune2fs.c      | 23 +++++++++++++++--------
>> 3 files changed, 33 insertions(+), 8 deletions(-)
>> 
>> diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
>> index 59fd9742..3a63b74d 100644
>> --- a/lib/ext2fs/ext2fs.h
>> +++ b/lib/ext2fs/ext2fs.h
>> @@ -1630,6 +1630,8 @@ extern int ext2fs_journal_sb_start(int blocksize);
>> extern errcode_t ext2fs_open(const char *name, int flags, int superblock,
>>                 unsigned int block_size, io_manager manager,
>>                 ext2_filsys *ret_fs);
>> +extern errcode_t ext2fs_read_sb(const char *name, io_manager manager,
>> +                struct ext2_super_block * super);
>> extern errcode_t ext2fs_open2(const char *name, const char *io_options,
>>                  int flags, int superblock,
>>                  unsigned int block_size, io_manager manager,
>> diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
>> index 51b54a44..95f45d84 100644
>> --- a/lib/ext2fs/openfs.c
>> +++ b/lib/ext2fs/openfs.c
>> @@ -99,6 +99,22 @@ static void block_sha_map_free_entry(void *data)
>>    return;
>> }
>> 
>> +errcode_t ext2fs_read_sb(const char *name, io_manager manager,
>> +             struct ext2_super_block * super)
>> +{
>> +    io_channel    io;
>> +    errcode_t    retval = 0;
>> +
>> +    retval = manager->open(name, 0, &io);
>> +    if (!retval) {
>> +        retval = io_channel_read_blk(io, 1, -SUPERBLOCK_SIZE,
>> +                     super);
>> +        io_channel_close(io);
>> +    }
>> +
>> +    return retval;
>> +}
>> +
>> /*
>> *  Note: if superblock is non-zero, block-size must also be non-zero.
>> *    Superblock and block_size can be zero to use the default size.
>> diff --git a/misc/tune2fs.c b/misc/tune2fs.c
>> index 7d2d38d7..fea607e1 100644
>> --- a/misc/tune2fs.c
>> +++ b/misc/tune2fs.c
>> @@ -2879,6 +2879,21 @@ int tune2fs_main(int argc, char **argv)
>> #endif
>>        io_ptr = unix_io_manager;
>> 
>> +    if (print_label) {
>> +        /* For e2label emulation */
>> +        struct ext2_super_block sb;
>> +
>> +        /* Read only superblock. Nothing else metters.*/
>> +        retval = ext2fs_read_sb(device_name, io_ptr, &sb);
>> +        if (!retval) {
>> +            printf("%.*s\n", (int) sizeof(sb.s_volume_name),
>> +                   sb.s_volume_name);
>> +        }
>> +
>> +        remove_error_table(&et_ext2_error_table);
>> +        return retval;
>> +    }
>> +
>> retry_open:
>>    if ((open_flag & EXT2_FLAG_RW) == 0 || f_flag)
>>        open_flag |= EXT2_FLAG_SKIP_MMP;
>> @@ -2972,14 +2987,6 @@ retry_open:
>>    sb = fs->super;
>>    fs->flags &= ~EXT2_FLAG_MASTER_SB_ONLY;
>> 
>> -    if (print_label) {
>> -        /* For e2label emulation */
>> -        printf("%.*s\n", (int) sizeof(sb->s_volume_name),
>> -               sb->s_volume_name);
>> -        remove_error_table(&et_ext2_error_table);
>> -        goto closefs;
>> -    }
>> -
>>    retval = ext2fs_check_if_mounted(device_name, &mount_flags);
>>    if (retval) {
>>        com_err("ext2fs_check_if_mount", retval,
>> -- 
>> 2.14.3
>> 
> 

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