Re: [PATCH v4] ceph: fix write_begin optimization when write is beyond EOF

On Sun, Jun 13, 2021 at 08:02:12AM -0400, Jeff Layton wrote:

...

• /* clamp length to end of the current page */
• if (len > PAGE_SIZE)

• len = PAGE_SIZE - offset;
  

Actually, I think this should be:

len = min(len, PAGE_SIZE - offset);

Otherwise, len could still go beyond the end of the page.

I don't understand why you want to clamp length instead of just coping with len being > PAGE_SIZE.

...

• /* full page write */
• if (offset == 0 && len == PAGE_SIZE)

• goto zero_out;
  

That becomes >=.

...

• /* zero-length file */
• if (i_size == 0)

• goto zero_out;
  

• /* position beyond last page in the file */
• if (index > ((i_size - 1) / PAGE_SIZE))

• goto zero_out;
  

• /* write that covers the the page from start to EOF or beyond it */
• if (offset == 0 && (pos + len) >= i_size)

• goto zero_out;
  

That doesn't need any change.

...

• return false;

+zero_out:

• zero_user_segments(page, 0, offset, offset + len, PAGE_SIZE);

That also doesn't need any change.