linux-kernel - Re: [PATCH] utimensat: AT_EMPTY

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Date:   Wed, 7 Nov 2018 13:05:15 -0500
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] utimensat: AT_EMPTY_PATH support

On Wed, Nov 07, 2018 at 10:15:52AM +0100, Miklos Szeredi wrote:
> This makes it possible to use utimensat on an O_PATH file (including
> symlinks).
> 
> It supersedes the nonstandard utimensat(fd, NULL, ...) form.
> 
> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>

Thanks for fixing this Miklos. It seems to work for me for following
use case I have where I want to change time on symlink opened with O_PATH.

symfd = open("foo-symlink.txt", O_PATH | O_NOFOLLOW);
utimensat(fd, "", NULL, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);

Thanks
Vivek

> ---
>  fs/utimes.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/utimes.c b/fs/utimes.c
> index bdcf2daf39c1..f9c7ebad19d7 100644
> --- a/fs/utimes.c
> +++ b/fs/utimes.c
> @@ -97,13 +97,13 @@ long do_utimes(int dfd, const char __user *filename, struct timespec64 *times,
>  		goto out;
>  	}
>  
> -	if (flags & ~AT_SYMLINK_NOFOLLOW)
> +	if (flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH))
>  		goto out;
>  
>  	if (filename == NULL && dfd != AT_FDCWD) {
>  		struct fd f;
>  
> -		if (flags & AT_SYMLINK_NOFOLLOW)
> +		if (flags)
>  			goto out;
>  
>  		f = fdget(dfd);
> @@ -119,6 +119,8 @@ long do_utimes(int dfd, const char __user *filename, struct timespec64 *times,
>  
>  		if (!(flags & AT_SYMLINK_NOFOLLOW))
>  			lookup_flags |= LOOKUP_FOLLOW;
> +		if (flags & AT_EMPTY_PATH)
> +			lookup_flags |= LOOKUP_EMPTY;
>  retry:
>  		error = user_path_at(dfd, filename, lookup_flags, &path);
>  		if (error)
> -- 
> 2.14.3
>