linux-kernel - Re: [patch -v2 06/23] s390/vmcp: use simple_read_from

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Message-Id: <200806021053.34647.borntraeger@de.ibm.com>
Date:	Mon, 2 Jun 2008 10:53:34 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	akinobu.mita@...il.com
Cc:	linux-kernel@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux390@...ibm.com, linux-s390@...r.kernel.org
Subject: Re: [patch -v2 06/23] s390/vmcp: use simple_read_from_buffer

Am Montag, 2. Juni 2008 schrieb akinobu.mita@...il.com:

> -	tocopy = min(session->resp_size - (size_t) (*ppos), count);
> -	tocopy = min(tocopy, session->bufsize - (size_t) (*ppos));
> +	ret = simple_read_from_buffer(buff, count, ppos,
> +				session->response, session->resp_size);
> 

Its not that simple. The z/VM Diagnose 8 has a quite interesting return value.

- session->bufsize is the size of the buffer as we allocated and know 
- session->resp_size is the size of the data - no matter if the buffer was 
large enough. z/VM is smart enough to not go beyond the buffer, but it tells 
us how many bytes it skipped. resp_size contains bufsize + skipped_bytes.

Unfortunately there is no end of string delimiter and we have to use the 
response size.

There are two cases:
1. The buffer was large enough, so we can use session->resp_size
2. The buffer was not large enough and output was truncated. we must now use 
session->bufsize

Christian
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