linux-kernel - Re: [PATCH] vfs: inline getname()

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Message-ID: <7exbpvo4svpmhk7n7sjq55wlaqhndk3qk2ijw7y4dvykqbhg3n@y5axd74zos5i>
Date: Thu, 6 Feb 2025 10:02:35 +0100
From: Jan Kara <jack@...e.cz>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: brauner@...nel.org, viro@...iv.linux.org.uk, jack@...e.cz, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] vfs: inline getname()

On Thu 06-02-25 01:01:05, Mateusz Guzik wrote:
> It is merely a trivial wrapper around getname_flags which adds a zeroed
> argument, no point paying for an extra call.
> 
> Signed-off-by: Mateusz Guzik <mjguzik@...il.com>

Well, the "extra call" in your changelog is a bit overrated. Such wrappers
get compiled into a constant jump anyway - e.g. in my kernel:

Dump of assembler code for function getname:
   0xffffffff815edb80 <+0>:	endbr64 
   0xffffffff815edb84 <+4>:	call   0xffffffff8131cad0 <__fentry__>
   0xffffffff815edb89 <+9>:	xor    %esi,%esi
   0xffffffff815edb8b <+11>:	jmp    0xffffffff815ed750 <getname_flags>

And the jmp to constant is practically free on current CPUs.

Overall inline function for this is I guess a more common way how we do
things like this so feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/namei.c         | 5 -----
>  include/linux/fs.h | 5 ++++-
>  2 files changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 3ab9440c5b93..3a4039acdb3f 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -218,11 +218,6 @@ struct filename *getname_uflags(const char __user *filename, int uflags)
>  	return getname_flags(filename, flags);
>  }
>  
> -struct filename *getname(const char __user * filename)
> -{
> -	return getname_flags(filename, 0);
> -}
> -
>  struct filename *__getname_maybe_null(const char __user *pathname)
>  {
>  	struct filename *name;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index e73d9b998780..85d88dd5ab6c 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2840,7 +2840,10 @@ extern int filp_close(struct file *, fl_owner_t id);
>  
>  extern struct filename *getname_flags(const char __user *, int);
>  extern struct filename *getname_uflags(const char __user *, int);
> -extern struct filename *getname(const char __user *);
> +static inline struct filename *getname(const char __user *name)
> +{
> +	return getname_flags(name, 0);
> +}
>  extern struct filename *getname_kernel(const char *);
>  extern struct filename *__getname_maybe_null(const char __user *);
>  static inline struct filename *getname_maybe_null(const char __user *name, int flags)
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR