linux-kernel - Re: [PATCH v5 1/3] FUSE: Avoid lookups in fuse create

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Date:   Wed, 18 May 2022 13:41:01 -0400
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Dharmendra Singh <dharamhans87@...il.com>
Cc:     miklos@...redi.hu, linux-fsdevel@...r.kernel.org,
        fuse-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        bschubert@....com, Dharmendra Singh <dsingh@....com>
Subject: Re: [PATCH v5 1/3] FUSE: Avoid lookups in fuse create

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.

Thanks
Vivek
>  
>  	/* CUSE specific operations */
>  	CUSE_INIT		= 4096,
> -- 
> 2.17.1
>