linux-kernel - [PATCH] xen: make sysfs files behave as their names suggest

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Message-ID: <4980FD4C.3030700@goop.org>
Date:	Wed, 28 Jan 2009 16:50:20 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Stable Kernel <stable@...nel.org>,
	"dan.magenheimer@...cle.com" <dan.magenheimer@...cle.com>
Subject: [PATCH] xen: make sysfs files behave as their names suggest

1: make "target_kb" only accept and produce a memory size in kilobytes.
2: add a second "target" file which produces output in bytes, and will accept
   memparse input (scaled bytes)

This fixes the rather irritating problem that writing the same value
read back into target_kb would end up shrinking the domain by a factor
of 1024, with generally bad results.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
 drivers/xen/balloon.c |   33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

===================================================================
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -586,7 +586,7 @@
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	target_bytes = memparse(buf, &endchar);
+	target_bytes = simple_strtoull(buf, &endchar, 0) * 1024;
 
 	balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 
@@ -596,8 +596,39 @@
 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR,
 		   show_target_kb, store_target_kb);
 
+
+static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr,
+			      char *buf)
+{
+	return sprintf(buf, "%llu\n",
+		       (u64)balloon_stats.target_pages << PAGE_SHIFT);
+}
+
+static ssize_t store_target(struct sys_device *dev,
+			    struct sysdev_attribute *attr,
+			    const char *buf,
+			    size_t count)
+{
+	char *endchar;
+	unsigned long long target_bytes;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	target_bytes = memparse(buf, &endchar);
+
+	balloon_set_new_target(target_bytes >> PAGE_SHIFT);
+
+	return count;
+}
+
+static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR,
+		   show_target, store_target);
+
+
 static struct sysdev_attribute *balloon_attrs[] = {
 	&attr_target_kb,
+	&attr_target,
 };
 
 static struct attribute *balloon_info_attrs[] = {


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