Re: [f2fs-dev] [PATCH v3] mkfs.f2fs: support -C [no]hashonly to control linear lookup fallback

[Chao Yu <chao@kernel.org>]

On 7/28/25 09:05, Zhiguo Niu wrote:
> Hi Chao
> 
> Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>
> 于2025年7月25日周五 13:51写道：
>>
>> It provides a way to disable linear lookup fallback during mkfs.
>>
>> Behavior summary:
>>                         Android         Distro
>> By default              disabled        enabled
>>
>> Android case:
>>
>> 1.1) Disable linear lookup:
>> - mkfs.f2fs -f -g android -O casefold -C utf8:hashonly /dev/vdb
>> - dump.f2fs -d3 /dev/vdb |grep s_encoding_flags
>> s_encoding_flags                        [0x       2 : 2]
>>
>> 1.2) Enable linear lookup:
>> - mkfs.f2fs -f -g android -O casefold -C utf8:nohashonly /dev/vdb
>> - dump.f2fs -d3 /dev/vdb |grep s_encoding_flags
>> s_encoding_flags                        [0x       0 : 0]
>>
>> 1.3) By default:
>> - mkfs.f2fs -f -g android -O casefold -C utf8 /dev/vdb
>> Info: set default linear_lookup option: disable
>> - dump.f2fs -d3 /dev/vdb |grep s_encoding_flags
>> s_encoding_flags                        [0x       2 : 2]
>>
>> Distro case:
>>
>> 2.1) Disable linear lookup:
>> - mkfs.f2fs -f -O casefold -C utf8:hashonly /dev/vdb
>> - dump.f2fs -d3 /dev/vdb |grep s_encoding_flags
>> s_encoding_flags                        [0x       2 : 2]
>>
>> 2.2) Enable linear lookup:
>> - mkfs.f2fs -f -O casefold -C utf8:nohashonly /dev/vdb
>> - dump.f2fs -d3 /dev/vdb |grep s_encoding_flags
>> s_encoding_flags                        [0x       0 : 0]
>>
>> 2.3) By default:
>> - mkfs.f2fs -f -O casefold -C utf8 /dev/vdb
>> - dump.f2fs -d3 /dev/vdb |grep s_encoding_flags
>> s_encoding_flags                        [0x       0 : 0]
>>
> It is very clear and easy to understand.
>> Signed-off-by: Chao Yu <chao@kernel.org>
>> ---
>> v3:
>> - honor [no]hashonly flag for Android case
>> - update testcase and output
>>  include/f2fs_fs.h       |  3 ++-
>>  lib/libf2fs.c           |  6 ++++++
>>  man/mkfs.f2fs.8         |  9 ++++++++-
>>  mkfs/f2fs_format.c      | 11 +++++++++++
>>  mkfs/f2fs_format_main.c |  3 ++-
>>  5 files changed, 29 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/f2fs_fs.h b/include/f2fs_fs.h
>> index f7268d1..a8da8fa 100644
>> --- a/include/f2fs_fs.h
>> +++ b/include/f2fs_fs.h
>> @@ -1478,7 +1478,8 @@ enum {
>>
>>  /* feature list in Android */
>>  enum {
>> -       F2FS_FEATURE_NAT_BITS = 0x0001,
>> +       F2FS_FEATURE_NAT_BITS           = 0x0001,
>> +       F2FS_FEATURE_LINEAR_LOOKUP      = 0x0002,
>>  };
>>
>>  /* nolinear lookup tune */
>> diff --git a/lib/libf2fs.c b/lib/libf2fs.c
>> index 2f012c8..1a496b7 100644
>> --- a/lib/libf2fs.c
>> +++ b/lib/libf2fs.c
>> @@ -1424,6 +1424,7 @@ static const struct enc_flags {
>>         char *param;
>>  } encoding_flags[] = {
>>         { F2FS_ENC_STRICT_MODE_FL, "strict" },
>> +       { F2FS_ENC_NO_COMPAT_FALLBACK_FL, "hashonly"}
>>  };
>>
>>  /* Return a positive number < 0xff indicating the encoding magic number
>> @@ -1485,6 +1486,11 @@ int f2fs_str2encoding_flags(char **param, __u16 *flags)
>>                                         *flags |= fl->flag;
>>                                 }
>>
>> +                               if (fl->flag == F2FS_ENC_NO_COMPAT_FALLBACK_FL)
>> +                                       c.nolinear_lookup = neg ?
>> +                                               LINEAR_LOOKUP_ENABLE :
>> +                                               LINEAR_LOOKUP_DISABLE;
>> +
>>                                 goto next_flag;
>>                         }
>>                 }
>> diff --git a/man/mkfs.f2fs.8 b/man/mkfs.f2fs.8
>> index 8b3b0cc..fcb227c 100644
>> --- a/man/mkfs.f2fs.8
>> +++ b/man/mkfs.f2fs.8
>> @@ -232,10 +232,17 @@ Use UTF-8 for casefolding.
>>  .I flags:
>>  .RS 1.2i
>>  .TP 1.2i
>> -.B strict
>> +.B [no]strict
>>  This flag specifies that invalid strings should be rejected by the filesystem.
>>  Default is disabled.
>>  .RE
>> +.RS 1.2i
>> +.TP 1.2i
>> +.B [no]hashonly
>> +This flag specifies that linear lookup fallback is off during lookup, to turn
>> +off linear lookup fallback, use nohashonly flag.
> here should "to turn off linear lookup fallback, use hashonly flag"?
> or "to turn on linear lookup fallback, use nohashonly flag"

Zhiguo,

Yes, it's typo, let me fix it, thanks for the review.

Thanks,

> 1.1) Disable linear lookup:
> - mkfs.f2fs -f -g android -O casefold -C utf8:hashonly /dev/vdb
> 
>> +For android case, it will disable linear lookup by default.
>> +.RE
>>  .RE
>>  .TP
>>  .BI \-q
>> diff --git a/mkfs/f2fs_format.c b/mkfs/f2fs_format.c
>> index 2680bd3..04dfc20 100644
>> --- a/mkfs/f2fs_format.c
>> +++ b/mkfs/f2fs_format.c
>> @@ -671,6 +671,17 @@ static int f2fs_prepare_super_block(void)
>>         memcpy(sb->init_version, c.version, VERSION_LEN);
>>
>>         if (c.feature & F2FS_FEATURE_CASEFOLD) {
>> +               /*
>> +                * if [no]hashonly option is not assigned, let's disable
>> +                * linear lookup fallback by default for Android case.
>> +                */
>> +               if ((c.nolinear_lookup == LINEAR_LOOKUP_DEFAULT) &&
>> +                       (c.disabled_feature & F2FS_FEATURE_LINEAR_LOOKUP)) {
>> +                       c.s_encoding_flags |= F2FS_ENC_NO_COMPAT_FALLBACK_FL;
>> +                       MSG(0, "Info: set default linear_lookup option: %s\n",
>> +                               c.s_encoding_flags & F2FS_ENC_NO_COMPAT_FALLBACK_FL ?
>> +                               "disable" : "enable");
>> +               }
>>                 set_sb(s_encoding, c.s_encoding);
>>                 set_sb(s_encoding_flags, c.s_encoding_flags);
>>         }
>> diff --git a/mkfs/f2fs_format_main.c b/mkfs/f2fs_format_main.c
>> index f0bec4f..8f8e975 100644
>> --- a/mkfs/f2fs_format_main.c
>> +++ b/mkfs/f2fs_format_main.c
>> @@ -143,7 +143,8 @@ static void add_default_options(void)
>>                 force_overwrite = 1;
>>                 c.wanted_sector_size = F2FS_BLKSIZE;
>>                 c.root_uid = c.root_gid = 0;
>> -               c.disabled_feature |= F2FS_FEATURE_NAT_BITS;
>> +               c.disabled_feature |= F2FS_FEATURE_NAT_BITS |
>> +                                       F2FS_FEATURE_LINEAR_LOOKUP;
>>
>>                 /* RO doesn't need any other features */
>>                 if (c.feature & F2FS_FEATURE_RO)
> others look OK to me,so
> Reviewed-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
>> --
>> 2.49.0
>>
>>
>>
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