Re: [Fwd: [PATCH] consolidate generic_writepages and mpage_writepages]

[Steve French (smfltc)]

> From: Miklos Szeredi <miklos@xxxxxxxxxx>
> To: akpm@xxxxxxxxxxxxxxxxxxxx
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
> Subject: [PATCH] consolidate generic_writepages and mpage_writepages
> Date: 	Fri, 16 Feb 2007 17:23:25 +0100
>
> From: Miklos Szeredi <mszeredi@xxxxxxx>
>
> Clean up massive code duplication between mpage_writepages() and
> generic_writepages().
>
> The new generic function, write_cache_pages() takes a function pointer
> argument, which will be called for each page to be written.
>
> Maybe cifs_writepages() too can use this infrastructure, but I'm not
> touching that with a ten-foot pole.
>  
The cifs case ought to be one of the simpler ones, pseudo-code is pretty 
easy, the hard part is all of the stuff unrelated to cifs:
Ideally if there were generic functions to help out, cifs writepages 
would look roughly like the following

cifs_writepages(struct address_space *mapping, struct writeback_control 
*wbc)
{
  
   while (no more pages to write) {
       /* find writeable file handle for this inode */
       /* find the biggest set of contiguous pages that total less than 
wsize */
       if (packet signing is enabled)
               /* write lock pages so they can not be changed under us 
while we are calculating the checksum */
     
      CIFSSMBWrite2(tree_connection, network_file_handle, array of 
iovecs, number of iovecs);

       if(packet signing was enabled)
               /* unlock pages */

       if(error) {
            set page errors
            if (mounted "hard" )
                  continue; /* retry */
            else /* if no retry possible */
                  return error to caller;
      }
       update bytes written statistics
       update index to point to next set of pages
   }  /* end while loop */
}


If it were even better, CIFSSMBWrite2 could be called async - so that it 
did not have to wait for a network response from Samba (just an ack from 
TCP), before issuing the next write onto the wire - but this would 
require that we could queue a pointer to a completion routine to the mpx 
entry.
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