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

[Chao Yu <ch...@ke...>]

On 7/24/2025 11:06 PM, Jaegeuk Kim wrote:
> Can we disable linear lookup by default, but add an option to enable it?

Sure.

> 
> On 07/24, Chao Yu wrote:
>> It provides a way to disable linear lookup fallback during mkfs.
>>
>> Usage:
>>
>> 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. 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]
>>
>> mkfs.f2fs -f -O casefold -C utf8 /dev/vdb
>> dump.f2fs -d3 /dev/vdb |grep s_encoding_flags
>> s_encoding_flags                        [0x       0 : 0]

Let me update the logic to disable linear lookup by default for case 2.2).

1)  mkfs.f2fs -f -O casefold -C utf8:hashonly /dev/vdb
2.1) mkfs.f2fs -f -O casefold -C utf8:nohashonly /dev/vdb
2.2) mkfs.f2fs -f -O casefold -C utf8 /dev/vdb

Thanks,

>>
>> Signed-off-by: Chao Yu <ch...@ke...>
>> ---
>>   lib/libf2fs.c   | 1 +
>>   man/mkfs.f2fs.8 | 8 +++++++-
>>   2 files changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/libf2fs.c b/lib/libf2fs.c
>> index 2f012c8..0e3e62a 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
>> diff --git a/man/mkfs.f2fs.8 b/man/mkfs.f2fs.8
>> index 8b3b0cc..b57f033 100644
>> --- a/man/mkfs.f2fs.8
>> +++ b/man/mkfs.f2fs.8
>> @@ -232,10 +232,16 @@ 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 there is no linear lookup fallback during lookup.
>> +By default, linear lookup fallback is enabled.
>> +.RE
>>   .RE
>>   .TP
>>   .BI \-q
>> -- 
>> 2.49.0