linux-kernel - Re: [PATCH] relay-file-read-start-pos-fix.patch

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Message-ID: <467750E9.4090808@hitachi.com>
Date:	Tue, 19 Jun 2007 12:43:37 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	David Wilder <dwilder@...ibm.com>, Tom Zanussi <zanussi@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, systemtap@...rces.redhat.com,
	Yumiko Sugita <yumiko.sugita.yf@...achi.com>,
	Satoshi Oshima <soshima@...hat.com>,
	Hideo Aoki <haoki@...hat.com>
Subject: Re: [PATCH] relay-file-read-start-pos-fix.patch

Hi David and Tom,

David Wilder wrote:
> This patch fixes a bug in the relay read interface causing the number
> of consumed bytes to be set incorrectly. 

Thank you. Your patch fixes one of my concerns.
However there is another bug I found.
When I use relayfs with "overwrite" mode, read() still set incorrect
number of consumed bytes.
I tried to fix that. Please review it.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

---
 kernel/relay.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Index: linux-2.6.22-rc4-mm2/kernel/relay.c
===================================================================
--- linux-2.6.22-rc4-mm2.orig/kernel/relay.c	2007-06-13 20:22:02.000000000 +0900
+++ linux-2.6.22-rc4-mm2/kernel/relay.c	2007-06-18 23:00:54.000000000 +0900
@@ -812,7 +812,10 @@
 	}

 	buf->bytes_consumed += bytes_consumed;
-	read_subbuf = read_pos / buf->chan->subbuf_size;
+	if (!read_pos)
+		read_subbuf = buf->subbufs_consumed;
+	else
+		read_subbuf = read_pos / buf->chan->subbuf_size;
 	if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
 		if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
 		    (buf->offset == subbuf_size))
@@ -841,8 +844,9 @@
 	}

 	if (unlikely(produced - consumed >= n_subbufs)) {
-		consumed = (produced / n_subbufs) * n_subbufs;
+		consumed = produced - n_subbufs + 1;
 		buf->subbufs_consumed = consumed;
+		buf->bytes_consumed = 0;
 	}
 	
 	produced = (produced % n_subbufs) * subbuf_size + buf->offset;



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