Re: nfsd: supports read buffer from multiples pages

[Kinglong Mee <kinglongmee@gmail.com>]

On 2/2/2016 02:38, J. Bruce Fields wrote:
> On Sun, Jan 31, 2016 at 08:50:10PM +0800, Kinglong Mee wrote:
>> ltp fsync02 will cause nfs sending LAYOUTCOMMIT with length
>> larger than two pages. nfsd returns NFSERR_BAD_XDR right now.
> 
> This is with the xfs block layout?

Yes, xfs block layout.
Tested by ltp's fsync02.

thanks,
Kinglong Mee
> 
> Christoph, do we know anything about average or worst-case sizes for
> that layout update field?
> 
>> This patch lets nfsd supports read buffer from multiples pages.
> 
> Hm.  We'll end up kmalloc()ing the passed-in field length:
> 
> 		p = argp->tmpp = kmalloc(nbytes, GFP_KERNEL);
> 
> We still do still have that (avail + argp->pagelen) limit, so we're not
> going to pass arbitrarily large nbytes straight from the network to
> kmalloc.  But we do try to avoid depending on higher-order allocations.
> 
> --b.
> 
>>
>> Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
>> ---
>>  fs/nfsd/nfs4xdr.c | 18 ++++++++++++++----
>>  1 file changed, 14 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
>> index d6ef095..fcf399f 100644
>> --- a/fs/nfsd/nfs4xdr.c
>> +++ b/fs/nfsd/nfs4xdr.c
>> @@ -143,11 +143,11 @@ static __be32 *read_buf(struct nfsd4_compoundargs *argp, u32 nbytes)
>>  	 * Maybe we need a new page, maybe we have just run out
>>  	 */
>>  	unsigned int avail = (char *)argp->end - (char *)argp->p;
>> +	unsigned int copied = 0;
>>  	__be32 *p;
>> +
>>  	if (avail + argp->pagelen < nbytes)
>>  		return NULL;
>> -	if (avail + PAGE_SIZE < nbytes) /* need more than a page !! */
>> -		return NULL;
>>  	/* ok, we can do it with the current plus the next page */
>>  	if (nbytes <= sizeof(argp->tmp))
>>  		p = argp->tmp;
>> @@ -164,9 +164,19 @@ static __be32 *read_buf(struct nfsd4_compoundargs *argp, u32 nbytes)
>>  	 * guarantee p points to at least nbytes bytes.
>>  	 */
>>  	memcpy(p, argp->p, avail);
>> +	copied += avail;
>> +	nbytes -= avail;
>> +
>> +	while (nbytes > PAGE_SIZE) {
>> +		next_decode_page(argp);
>> +		memcpy(((char*)p) + copied, argp->p, PAGE_SIZE);
>> +		copied += PAGE_SIZE;
>> +		nbytes -= PAGE_SIZE;
>> +	}
>> +
>>  	next_decode_page(argp);
>> -	memcpy(((char*)p)+avail, argp->p, (nbytes - avail));
>> -	argp->p += XDR_QUADLEN(nbytes - avail);
>> +	memcpy(((char*)p) + copied, argp->p, nbytes);
>> +	argp->p += XDR_QUADLEN(nbytes);
>>  	return p;
>>  }
>>  
>> -- 
>> 2.5.0
>