[5/4] 9p: pass the correct prototype to read_cache_page
diff mbox series

Message ID 20190501173443.GA19969@lst.de
State New
Headers show
Series
  • [1/4] mm: fix an overly long line in read_cache_page
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Commit Message

Christoph Hellwig May 1, 2019, 5:34 p.m. UTC
Fix the callback 9p passes to read_cache_page to actually have the
proper type expected.  Casting around function pointers can easily
hide typing bugs, and defeats control flow protection.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/9p/vfs_addr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

William Kucharski May 2, 2019, 6:08 a.m. UTC | #1
1) You need to pass "filp" rather than "filp->private_data" to read_cache_pages()
in v9fs_fid_readpage().

The patched code passes "filp->private_data" as the "data" parameter to
read_cache_pages(), which would generate a call to:

    filler(data, page)

which would become a call to:

static int v9fs_vfs_readpage(struct file *filp, struct page *page)
{	
        return v9fs_fid_readpage(filp->private_data, page);
}

which would then effectively become:

    v9fs_fid_readpage(filp->private_data->private_data, page)

Which isn't correct; because data is a void *, no error is thrown when
v9fs_vfs_readpages treats filp->private_data as if it is filp.


2) I'd also like to see an explicit comment in do_read_cache_page() along
the lines of:

/*
 * If a custom page filler was passed in use it, otherwise use the
 * standard readpage() routine defined for the address_space.
 *
 */

3) Patch 5/4?

Otherwise it looks good.

Reviewed-by: William Kucharski <william.kucharski@oracle.com>

> On May 1, 2019, at 11:34 AM, Christoph Hellwig <hch@lst.de> wrote:
> 
> Fix the callback 9p passes to read_cache_page to actually have the
> proper type expected.  Casting around function pointers can easily
> hide typing bugs, and defeats control flow protection.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> fs/9p/vfs_addr.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
> index 0bcbcc20f769..02e0fc51401e 100644
> --- a/fs/9p/vfs_addr.c
> +++ b/fs/9p/vfs_addr.c
> @@ -50,8 +50,9 @@
>  * @page: structure to page
>  *
>  */
> -static int v9fs_fid_readpage(struct p9_fid *fid, struct page *page)
> +static int v9fs_fid_readpage(void *data, struct page *page)
> {
> +	struct p9_fid *fid = data;
> 	struct inode *inode = page->mapping->host;
> 	struct bio_vec bvec = {.bv_page = page, .bv_len = PAGE_SIZE};
> 	struct iov_iter to;
> @@ -122,7 +123,8 @@ static int v9fs_vfs_readpages(struct file *filp, struct address_space *mapping,
> 	if (ret == 0)
> 		return ret;
> 
> -	ret = read_cache_pages(mapping, pages, (void *)v9fs_vfs_readpage, filp);
> +	ret = read_cache_pages(mapping, pages, v9fs_fid_readpage,
> +			filp->private_data);
> 	p9_debug(P9_DEBUG_VFS, "  = %d\n", ret);
> 	return ret;
> }
Matthew Wilcox May 2, 2019, 10:20 a.m. UTC | #2
On Thu, May 02, 2019 at 12:08:29AM -0600, William Kucharski wrote:
> 3) Patch 5/4?

That's a relatively common notation when an extra patch is needed to fix
something after a series has been sent ;-)
Christoph Hellwig May 2, 2019, 1:04 p.m. UTC | #3
On Thu, May 02, 2019 at 12:08:29AM -0600, William Kucharski wrote:
> 1) You need to pass "filp" rather than "filp->private_data" to read_cache_pages()
> in v9fs_fid_readpage().

With this patch v9fs_fid_readpage takes a void pointer that must be
a FID, and we pass the FID everywhere:

 - v9fs_vfs_readpage passes filp->private_data
 - v9fs_vfs_readpages passes filp->private_data through
   read_cache_pages
 - v9fs_write_begin passes the local fid variable


> 
> The patched code passes "filp->private_data" as the "data" parameter to
> read_cache_pages(), which would generate a call to:
> 
>     filler(data, page)
> 
> which would become a call to:
> 
> static int v9fs_vfs_readpage(struct file *filp, struct page *page)
> {	
>         return v9fs_fid_readpage(filp->private_data, page);
> }

Except that we don't pass v9fs_vfs_readpage as the filler any more,
we now pass v9fs_fid_readpage.
William Kucharski May 2, 2019, 2:01 p.m. UTC | #4
> On May 2, 2019, at 7:04 AM, Christoph Hellwig <hch@lst.de> wrote:
> 
> Except that we don't pass v9fs_vfs_readpage as the filler any more,
> we now pass v9fs_fid_readpage.

True, so never mind. :-)

Patch
diff mbox series

diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index 0bcbcc20f769..02e0fc51401e 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -50,8 +50,9 @@ 
  * @page: structure to page
  *
  */
-static int v9fs_fid_readpage(struct p9_fid *fid, struct page *page)
+static int v9fs_fid_readpage(void *data, struct page *page)
 {
+	struct p9_fid *fid = data;
 	struct inode *inode = page->mapping->host;
 	struct bio_vec bvec = {.bv_page = page, .bv_len = PAGE_SIZE};
 	struct iov_iter to;
@@ -122,7 +123,8 @@  static int v9fs_vfs_readpages(struct file *filp, struct address_space *mapping,
 	if (ret == 0)
 		return ret;
 
-	ret = read_cache_pages(mapping, pages, (void *)v9fs_vfs_readpage, filp);
+	ret = read_cache_pages(mapping, pages, v9fs_fid_readpage,
+			filp->private_data);
 	p9_debug(P9_DEBUG_VFS, "  = %d\n", ret);
 	return ret;
 }