linux-kernel - Re: [RFC 1/3] include/linux.h: Factor out generic platform_test_fs

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Message-ID: <20241211180902.GA6678@frogsfrogsfrogs>
Date: Wed, 11 Dec 2024 10:09:02 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc: linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
	Ritesh Harjani <ritesh.list@...il.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Andrey Albershteyn <aalbersh@...nel.org>,
	John Garry <john.g.garry@...cle.com>
Subject: Re: [RFC 1/3] include/linux.h: Factor out generic
 platform_test_fs_fd() helper

On Wed, Dec 11, 2024 at 01:24:02PM +0530, Ojaswin Mujoo wrote:
> Factor our the generic code to detect the FS type out of
> platform_test_fs_fd(). This can then be used to detect different file
> systems types based on magic number.
> 
> Also, add a helper to detect if the fd is from an ext4 filesystem.
> 
> Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> ---
>  include/linux.h | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux.h b/include/linux.h
> index e9eb7bfb26a1..52c64014c57f 100644
> --- a/include/linux.h
> +++ b/include/linux.h
> @@ -43,13 +43,7 @@ static __inline__ int xfsctl(const char *path, int fd, int cmd, void *p)
>  	return ioctl(fd, cmd, p);
>  }
>  
> -/*
> - * platform_test_xfs_*() implies that xfsctl will succeed on the file;
> - * on Linux, at least, special files don't get xfs file ops,
> - * so return 0 for those
> - */
> -
> -static __inline__ int platform_test_xfs_fd(int fd)
> +static __inline__ int platform_test_fs_fd(int fd, long type)
>  {
>  	struct statfs statfsbuf;
>  	struct stat statbuf;
> @@ -60,7 +54,22 @@ static __inline__ int platform_test_xfs_fd(int fd)
>  		return 0;
>  	if (!S_ISREG(statbuf.st_mode) && !S_ISDIR(statbuf.st_mode))
>  		return 0;
> -	return (statfsbuf.f_type == 0x58465342);	/* XFSB */
> +	return (statfsbuf.f_type == type);
> +}
> +
> +/*
> + * platform_test_xfs_*() implies that xfsctl will succeed on the file;
> + * on Linux, at least, special files don't get xfs file ops,
> + * so return 0 for those
> + */
> +static __inline__ int platform_test_xfs_fd(int fd)
> +{
> +	return platform_test_fs_fd(fd, 0x58465342); /* XFSB */
> +}
> +
> +static __inline__ int platform_test_ext4_fd(int fd)
> +{
> +	return platform_test_fs_fd(fd, 0xef53); /* EXT4 magic number */

Should this be pulling EXT4_SUPER_MAGIC from linux/magic.h?

--D

>  }
>  
>  static __inline__ int platform_test_xfs_path(const char *path)
> -- 
> 2.43.5
> 
>