Hello Herbert,

Thank you for your quick response.

Herbert Xu wrote:

On Tue, Mar 25, 2008 at 02:39:04PM -0400, Hideo AOKI wrote:

quoted

Current pskb_expand_head() doesn't change truesize, while it
reallocates memory. Then, if argument nhead or ntail aren't 0, caller
must update truesize.

We had this bug at audit_expand() in January and fixed it as commit
406a1d868001423c85a3165288e566e65f424fe6. However, some drivers and
subsystems still use pskb_expand_head() without updating truesize.

Drivers usually aren't supposed to change truesize so doing
this would actually create bugs.

I understood your point. 

Since keeping correct truesize is important to network memory
accounting, I want to fix network subsystem part at least.

I think that it is inconvenient for caller functions to need
updateing truesize by themselves. How about this change to
avoid the inconvenience?

 - Current implementation is renamed to __pskb_expand_head().
 - Drivers call __pskb_expand_head() instead of pskb_expand_head().
 - New pskb_expand_head() updates truesize after calling 
  __pskb_expand_head(). 

Or, should I simply add truesize calculation after
pskb_expand_head() calls which change truesize?
 

quoted

In addition, there is another problem to update truesise. Since
pskb_expand_head() aligns memory size before reallocation, caller
functions may not update turesize correctly if they just add nhaad
and ntail to turesize.

That should be fixable by making sure that nhead + ntail is
aligned.

I see.

Regards,
Hideo

-- 
Hitachi Computer Products (America) Inc.