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

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Message-ID: <961aa3350806020528t4224f435qfb8406328c38c33f@mail.gmail.com>
Date:	Mon, 2 Jun 2008 21:28:48 +0900
From:	"Akinobu Mita" <akinobu.mita@...il.com>
To:	"Christian Borntraeger" <borntraeger@...ibm.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

2008/6/2 Christian Borntraeger <borntraeger@...ibm.com>:
> 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

Thanks. I made too much simplified the original code.
So I'll change these lines to be

size_t size = min_t(size_t, session->resp_size, session->bufsize);
ret = simple_read_from_buffer(buff, count, ppos, session->response, size);
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