[lxc-devel] [lxcfs/master] uptime: fix a problem with subsequent reads.

[bmiklautz on Github]

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From bbdf646b5e0c3f300c50776a85d2f805fd3aef45 Mon Sep 17 00:00:00 2001
From: Bernhard Miklautz <bernhard.miklautz at shacknet.at>
Date: Thu, 3 Aug 2017 13:37:37 +0200
Subject: [PATCH] uptime: fix a problem with subsequent reads.

When doing subsequent reads of uptime on an open file handle
in the form:

read
lseek 0L, SEEK_SET
read

the second (and later) reads cause that the error
"failed to write to cache" was printed. This
happens for example with "top". top would print the error:

bad data in /proc/uptime

To fix this problem use the whole size of the buffer instead of the d->size
because this is set on the first read.

This behavior was introduced with commit 0ecddf023a4caf8e8d2fe7e9125d777a06c5ec12.

Signed-off-by: Bernhard Miklautz <bernhard.miklautz at shacknet.at>
---
 bindings.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/bindings.c b/bindings.c
index 1442b9a..d7c2d1d 100644
--- a/bindings.c
+++ b/bindings.c
@@ -3842,10 +3842,10 @@ static int proc_uptime_read(char *buf, size_t size, off_t offset,
 #endif
 
 	if (offset){
-		if (offset > d->size)
-			return -EINVAL;
 		if (!d->cached)
 			return 0;
+		if (offset > d->size)
+			return -EINVAL;
 		int left = d->size - offset;
 		total_len = left > size ? size: left;
 		memcpy(buf, cache + offset, total_len);
@@ -3860,8 +3860,8 @@ static int proc_uptime_read(char *buf, size_t size, off_t offset,
 	if (reaperage >= busytime)
 		idletime = reaperage - busytime;
 
-	total_len = snprintf(d->buf, d->size, "%"PRIu64".00 %"PRIu64".00\n", reaperage, idletime);
-	if (total_len < 0 || total_len >=  d->size){
+	total_len = snprintf(d->buf, d->buflen, "%"PRIu64".00 %"PRIu64".00\n", reaperage, idletime);
+	if (total_len < 0 || total_len >=  d->buflen){
 		lxcfs_error("%s\n", "failed to write to cache");
 		return 0;
 	}