Re: [f2fs-dev] [PATCH v3] mkfs.f2fs: support -C [no]hashonly to control linear lookup fallback
From: Chao Yu
Date: Sun Jul 27 2025 - 22:03:04 EST
On 7/28/25 09:05, Zhiguo Niu wrote:
> Hi Chao
>
> Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx>
> 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@xxxxxxxxxx>
>> ---
>> 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@xxxxxxxxxx>
>> --
>> 2.49.0
>>
>>
>>
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