linux-ext4 - Re: [PATCH v2] fs: ext4: support relative path for `journal

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Message-ID: <20240925075105.lnssx7gcgfh5s743@quack3>
Date: Wed, 25 Sep 2024 09:51:05 +0200
From: Jan Kara <jack@...e.cz>
To: Hongbo Li <lihongbo22@...wei.com>
Cc: tytso@....edu, adilger.kernel@...ger.ca, viro@...iv.linux.org.uk,
	brauner@...nel.org, jack@...e.cz, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, chris.zjh@...wei.com
Subject: Re: [PATCH v2] fs: ext4: support relative path for `journal_path` in
 mount option.

On Wed 25-09-24 09:56:24, Hongbo Li wrote:
> The `fs_lookup_param` did not consider the relative path for
> block device. When we mount ext4 with `journal_path` option using
> relative path, `param->dirfd` was not set which will cause mounting
> error.
> 
> This can be reproduced easily like this:
> 
> mke2fs -F -O journal_dev $JOURNAL_DEV -b 4096 100M
> mkfs.ext4 -F -J device=$JOURNAL_DEV -b 4096 $FS_DEV
> cd /dev; mount -t ext4 -o journal_path=`basename $JOURNAL_DEV` $FS_DEV $MNT
> 
> Fixes: 461c3af045d3 ("ext4: Change handle_mount_opt() to use fs_parameter")
> Suggested-by: Christian Brauner <brauner@...nel.org>
> Signed-off-by: Hongbo Li <lihongbo22@...wei.com>
> ---
> v2:
>   - Change the journal_path parameter as string not bdev, and
>     determine the relative path situation inside fs_lookup_param.
>   - Add Suggested-by.
> 
> v1: https://lore.kernel.org/all/20240527-mahlen-packung-3fe035ab390d@brauner/
> ---
>  fs/ext4/super.c | 4 ++--
>  fs/fs_parser.c  | 3 +++
>  2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 16a4ce704460..cd23536ce46e 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1744,7 +1744,7 @@ static const struct fs_parameter_spec ext4_param_specs[] = {
>  	fsparam_u32	("min_batch_time",	Opt_min_batch_time),
>  	fsparam_u32	("max_batch_time",	Opt_max_batch_time),
>  	fsparam_u32	("journal_dev",		Opt_journal_dev),
> -	fsparam_bdev	("journal_path",	Opt_journal_path),
> +	fsparam_string	("journal_path",	Opt_journal_path),

Why did you change this? As far as I can see the only effect would be that
empty path will not be allowed (which makes sense) but that seems like an
independent change which would deserve a comment in the changelog? Or am I
missing something?

>  	fsparam_flag	("journal_checksum",	Opt_journal_checksum),
>  	fsparam_flag	("nojournal_checksum",	Opt_nojournal_checksum),
>  	fsparam_flag	("journal_async_commit",Opt_journal_async_commit),
> @@ -2301,7 +2301,7 @@ static int ext4_parse_param(struct fs_context *fc, struct fs_parameter *param)
>  			return -EINVAL;
>  		}
>  
> -		error = fs_lookup_param(fc, param, 1, LOOKUP_FOLLOW, &path);
> +		error = fs_lookup_param(fc, param, true, LOOKUP_FOLLOW, &path);
>  		if (error) {
>  			ext4_msg(NULL, KERN_ERR, "error: could not find "
>  				 "journal device path");
> diff --git a/fs/fs_parser.c b/fs/fs_parser.c
> index 24727ec34e5a..2ae296764b69 100644
> --- a/fs/fs_parser.c
> +++ b/fs/fs_parser.c
> @@ -156,6 +156,9 @@ int fs_lookup_param(struct fs_context *fc,
>  		f = getname_kernel(param->string);
>  		if (IS_ERR(f))
>  			return PTR_ERR(f);
> +		/* for relative path */
> +		if (f->name[0] != '/')
> +			param->dirfd = AT_FDCWD;

What Al meant is that you can do simply:
		param->dirfd = AT_FDCWD;

and everything will work the same because 'dfd' is ignored for absolute
pathnames in path_init().

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR