linux-kernel - Re: [PATCH v2] ext2: Handle fiemap on empty files to prevent EINVAL

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Message-ID: <aEytOcFNAI7ZcxzM@MiWiFi-CR6608-srv>
Date: Fri, 13 Jun 2025 18:59:05 -0400
From: Wei Gao <wegao@...e.com>
To: Jan Kara <jack@...e.cz>
Cc: linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2] ext2: Handle fiemap on empty files to prevent EINVAL

On Fri, Jun 13, 2025 at 11:42:17AM +0200, Jan Kara wrote:
> On Fri 13-06-25 11:18:38, Wei Gao wrote:
> > Previously, ext2_fiemap would unconditionally apply "len = min_t(u64, len,
> > i_size_read(inode));", When inode->i_size was 0 (for an empty file), this
> > would reduce the requested len to 0. Passing len = 0 to iomap_fiemap could
> > then result in an -EINVAL error, even for valid queries on empty files.
> > 
> > Link: https://github.com/linux-test-project/ltp/issues/1246
> > Signed-off-by: Wei Gao <wegao@...e.com>
> 
> ...
> 
> > diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> > index 30f8201c155f..591db2b4390a 100644
> > --- a/fs/ext2/inode.c
> > +++ b/fs/ext2/inode.c
> > @@ -895,9 +895,15 @@ int ext2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> >  		u64 start, u64 len)
> >  {
> >  	int ret;
> > +	u64 i_size;
> >  
> >  	inode_lock(inode);
> > -	len = min_t(u64, len, i_size_read(inode));
> > +
> > +	i_size = i_size_read(inode);
> > +
> > +	if (i_size > 0)
> > +		len = min_t(u64, len, i_size_read(inode));
> 
> 
> Thanks! This would actually lead to excessively slow fiemap for 0-length
> files. So what I've ended up with is attached modification of your patch.
Thank you for your patient review, I really appreciate it. 

BTW i have stupid question:
Where can I see the real-time status of this patch? such as whether it has been merged?
I have checked https://patchwork.kernel.org/project/linux-fsdevel/list/
but do not find current patch, maybe this patch need specific sent it to
linux-fsdevel@...r.kernel.org? I just get maillist through scripts/get_maintainer.pl but
mail list not contain linux-fsdevel@...r.kernel.org.

> 
> > +
> >  	ret = iomap_fiemap(inode, fieinfo, start, len, &ext2_iomap_ops);
> >  	inode_unlock(inode);
> >  
> > -- 
> > 2.49.0
> > 
> -- 
> Jan Kara <jack@...e.com>
> SUSE Labs, CR
> ---
> 
> From a099b09a3342a0b28ea330e405501b5b4d0424b4 Mon Sep 17 00:00:00 2001
> From: Wei Gao <wegao@...e.com>
> Date: Fri, 13 Jun 2025 11:18:38 -0400
> Subject: [PATCH] ext2: Handle fiemap on empty files to prevent EINVAL
> 
> Previously, ext2_fiemap would unconditionally apply "len = min_t(u64, len,
> i_size_read(inode));", When inode->i_size was 0 (for an empty file), this
> would reduce the requested len to 0. Passing len = 0 to iomap_fiemap could
> then result in an -EINVAL error, even for valid queries on empty files.
> 
> Link: https://github.com/linux-test-project/ltp/issues/1246
> Signed-off-by: Wei Gao <wegao@...e.com>
> Signed-off-by: Jan Kara <jack@...e.cz>
> Link: https://patch.msgid.link/20250613152402.3432135-1-wegao@suse.com
> ---
>  fs/ext2/inode.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> index 30f8201c155f..177b1f852b63 100644
> --- a/fs/ext2/inode.c
> +++ b/fs/ext2/inode.c
> @@ -895,9 +895,19 @@ int ext2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>  		u64 start, u64 len)
>  {
>  	int ret;
> +	loff_t i_size;
>  
>  	inode_lock(inode);
> -	len = min_t(u64, len, i_size_read(inode));
> +	i_size = i_size_read(inode);
> +	/*
> +	 * iomap_fiemap() returns EINVAL for 0 length. Make sure we don't trim
> +	 * length to 0 but still trim the range as much as possible since
> +	 * ext2_get_blocks() iterates unmapped space block by block which is
> +	 * slow.
> +	 */
> +	if (i_size == 0)
> +		i_size = 1;
> +	len = min_t(u64, len, i_size);
>  	ret = iomap_fiemap(inode, fieinfo, start, len, &ext2_iomap_ops);
>  	inode_unlock(inode);
>  
> -- 
> 2.43.0
>