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SubjectRe: [PATCH v5 1/3] FUSE: Avoid lookups in fuse create
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On 5/18/22 19:44, Vivek Goyal wrote:
> On Wed, May 18, 2022 at 01:41:02PM -0400, Vivek Goyal wrote:
>> On Tue, May 17, 2022 at 03:37:42PM +0530, Dharmendra Singh wrote:
>>
>> [..]
>>> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
>>> index d6ccee961891..bebe4be3f1cb 100644
>>> --- a/include/uapi/linux/fuse.h
>>> +++ b/include/uapi/linux/fuse.h
>>> @@ -301,6 +301,7 @@ struct fuse_file_lock {
>>> * FOPEN_CACHE_DIR: allow caching this directory
>>> * FOPEN_STREAM: the file is stream-like (no file position at all)
>>> * FOPEN_NOFLUSH: don't flush data cache on close (unless FUSE_WRITEBACK_CACHE)
>>> + * FOPEN_FILE_CREATED: the file was actually created
>>> */
>>> #define FOPEN_DIRECT_IO (1 << 0)
>>> #define FOPEN_KEEP_CACHE (1 << 1)
>>> @@ -308,6 +309,7 @@ struct fuse_file_lock {
>>> #define FOPEN_CACHE_DIR (1 << 3)
>>> #define FOPEN_STREAM (1 << 4)
>>> #define FOPEN_NOFLUSH (1 << 5)
>>> +#define FOPEN_FILE_CREATED (1 << 6)
>>>
>>> /**
>>> * INIT request/reply flags
>>> @@ -537,6 +539,7 @@ enum fuse_opcode {
>>> FUSE_SETUPMAPPING = 48,
>>> FUSE_REMOVEMAPPING = 49,
>>> FUSE_SYNCFS = 50,
>>> + FUSE_CREATE_EXT = 51,
>>
>> I am wondering if we really have to introduce a new opcode for this. Both
>> FUSE_CREATE and FUSE_CREATE_EXT prepare and send fuse_create_in{} and
>> expect fuse_entry_out and fuse_open_out in response. So no new structures
>> are being added. Only thing FUSE_CREATE_EXT does extra is that it also
>> reports back whether file was actually created or not.
>>
>> May be instead of adding an new fuse_opcode, we could simply add a
>> new flag which we send in fuse_create_in and that reqeusts to report
>> if file was created or not. This is along the lines of
>> FUSE_OPEN_KILL_SUIDGID.
>>
>> So say, a new flag FUSE_OPEN_REPORT_CREATE flag. Which we will set in
>> fuse_create_in->open_flags. If file server sees this flag is set, it
>> knows that it needs to set FOPEN_FILE_CREATED flag in response.
>>
>> To me creating a new flag FUSE_OPEN_REPORT_CREATE seems better instead
>> of adding a new opcode.
>
> Actually I take that back. If we were to use a flag, then we will have to
> do feature negotiation in advance at init time and only then we can set
> FUSE_OPEN_REPORT_CREATE. But we are relying on no new feature bit instead
> -ENOSYS will be returned if server does not support FUSE_CREATE_EXT.
> So adding a new opcode is better.

I guess it might work, if a flag is set and also returned (I would then
call it FUSE_CREATE_EXT) - user space creat would need to set
FOPEN_FILE_CREATED and that new flag. I just doubt that it simplifies
things.

Btw, thanks a lot for your thorough reviews! Much appreciated.


Thanks,
Bernd

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