[Virtio-fs] [PATCH 5/9] fuse: do not write whole page while page straddles i_size

[Liu Bo]

On Tue, Apr 16, 2019 at 04:16:21PM -0400, Vivek Goyal wrote:
> On Wed, Apr 17, 2019 at 02:03:18AM +0800, Liu Bo wrote:
> > From: Xiaoguang Wang <xiaoguang.wang at linux.alibaba.com>
> > 
> > If page straddles i_size and we write the whole page, the fuse
> > user-space filesystem may extend file size, it will confuse users.
> > 
> > Before this patch:
> > xfs_io -t -f \
> >         -c "truncate 5120" \
> >         -c "pwrite -S 0x58 0 5120"      \
> >         -c "mmap -rw 0 5120"            \
> >         -c "mwrite -S 0x59 2048 3072" \
> >         -c "close"      \
> >         testfile
> > testfile's length will be 8192 bytes, with this patch, testfile's
> > length will be 5120 bytes.
> > 
> > Reviewed-by: Joseph Qi <joseph.qi at linux.alibaba.com>
> > Signed-off-by: Xiaoguang Wang <xiaoguang.wang at linux.alibaba.com>
> 
> [cc miklos]
> 
> This sounds like a generic fuse issue as well (and not virtio-fs specic)?
> If yes, can you please send this fix separately to miklos and fuse
> mailing list.

Sure, will do.

thanks,
-liubo

> 
> Vivek
> > ---
> >  fs/fuse/file.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > index bb45acc..c6090f5 100644
> > --- a/fs/fuse/file.c
> > +++ b/fs/fuse/file.c
> > @@ -2293,6 +2293,8 @@ static int fuse_writepages_fill(struct page *page,
> >  	struct page *tmp_page;
> >  	bool is_writeback;
> >  	int err;
> > +	loff_t size;
> > +	unsigned int len;
> >  
> >  	if (!data->ff) {
> >  		err = -EIO;
> > @@ -2364,7 +2366,12 @@ static int fuse_writepages_fill(struct page *page,
> >  	copy_highpage(tmp_page, page);
> >  	req->pages[req->num_pages] = tmp_page;
> >  	req->page_descs[req->num_pages].offset = 0;
> > -	req->page_descs[req->num_pages].length = PAGE_SIZE;
> > +	size = i_size_read(inode);
> > +	if (page->index == size >> PAGE_SHIFT)
> > +		len = size & ~PAGE_MASK;
> > +	else
> > +		len = PAGE_SIZE;
> > +	req->page_descs[req->num_pages].length = len;
> >  
> >  	inc_wb_stat(&inode_to_bdi(inode)->wb, WB_WRITEBACK);
> >  	inc_node_page_state(tmp_page, NR_WRITEBACK_TEMP);
> > -- 
> > 1.8.3.1
> > 
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