From: Kay Sievers <kay.sievers@vrfy.org>
To: Greg KH <greg@kroah.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Lennart Poettering <lennart@poettering.net>
Subject: printk: /dev/kmsg - properly support writev() to avoid interleaved printk() lines
Date: Thu, 07 Apr 2011 04:29:20 +0200 [thread overview]
Message-ID: <1302143360.1143.3.camel@zag> (raw)
From: Kay Sievers <kay.sievers@vrfy.org>
printk: /dev/kmsg - properly support writev() to avoid interleaved printk lines
We should avoid calling printk() in a loop, when we pass a single
string to /dev/kmsg with writev().
Cc: Lennart Poettering <lennart@poettering.net>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
---
mem.c | 41 ++++++++++++++++++++++++++---------------
1 file changed, 26 insertions(+), 15 deletions(-)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 436a990..78923a9 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -806,29 +806,40 @@ static const struct file_operations oldmem_fops = {
};
#endif
-static ssize_t kmsg_write(struct file *file, const char __user *buf,
- size_t count, loff_t *ppos)
+static ssize_t kmsg_writev(struct kiocb *iocb, const struct iovec *iv,
+ unsigned long count, loff_t pos)
{
- char *tmp;
- ssize_t ret;
+ char *line, *p;
+ int len, i;
+ ssize_t ret = -EFAULT;
- tmp = kmalloc(count + 1, GFP_KERNEL);
- if (tmp == NULL)
+ len = iov_length(iv, count);
+ line = p = kmalloc(len + 1, GFP_KERNEL);
+ if (line == NULL)
return -ENOMEM;
- ret = -EFAULT;
- if (!copy_from_user(tmp, buf, count)) {
- tmp[count] = 0;
- ret = printk("%s", tmp);
- if (ret > count)
- /* printk can add a prefix */
- ret = count;
+
+ /*
+ * copy all vectors into a single string, to ensure we do
+ * not interleave our log line with other printk calls
+ */
+ for (i = 0; i < count; i++) {
+ if (copy_from_user(p, iv[i].iov_base, iv[i].iov_len))
+ goto out;
+ p += iv[i].iov_len;
}
- kfree(tmp);
+ p[0] = '\0';
+
+ ret = printk("%s", line);
+ /* printk can add a prefix */
+ if (ret > len)
+ ret = len;
+out:
+ kfree(line);
return ret;
}
static const struct file_operations kmsg_fops = {
- .write = kmsg_write,
+ .aio_write = kmsg_writev,
.llseek = noop_llseek,
};
next reply other threads:[~2011-04-07 2:30 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-07 2:29 Kay Sievers [this message]
2011-04-12 23:13 ` printk: /dev/kmsg - properly support writev() to avoid interleaved printk() lines Andrew Morton
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