linux-kernel - [PATCH] mm: add strictlimit knob

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 01 Nov 2013 18:31:40 +0400
From:	Maxim Patlasov <MPatlasov@...allels.com>
To:	karl.kiniger@....ge.com
Cc:	jack@...e.cz, linux-kernel@...r.kernel.org, t.artem@...os.com,
	linux-mm@...ck.org, mgorman@...e.de, tytso@....edu,
	akpm@...ux-foundation.org, fengguang.wu@...el.com,
	torvalds@...ux-foundation.org, mpatlasov@...allels.com
Subject: [PATCH] mm: add strictlimit knob

"strictlimit" feature was introduced to enforce per-bdi dirty limits for
FUSE which sets bdi max_ratio to 1% by default:

http://www.http.com//article.gmane.org/gmane.linux.kernel.mm/105809

However the feature can be useful for other relatively slow or untrusted
BDIs like USB flash drives and DVD+RW. The patch adds a knob to enable the
feature:

echo 1 > /sys/class/bdi/X:Y/strictlimit

Being enabled, the feature enforces bdi max_ratio limit even if global (10%)
dirty limit is not reached. Of course, the effect is not visible until
max_ratio is decreased to some reasonable value.

Signed-off-by: Maxim Patlasov <MPatlasov@...allels.com>
---
 mm/backing-dev.c |   35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index ce682f7..4ee1d64 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -234,11 +234,46 @@ static ssize_t stable_pages_required_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(stable_pages_required);
 
+static ssize_t strictlimit_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct backing_dev_info *bdi = dev_get_drvdata(dev);
+	unsigned int val;
+	ssize_t ret;
+
+	ret = kstrtouint(buf, 10, &val);
+	if (ret < 0)
+		return ret;
+
+	switch (val) {
+	case 0:
+		bdi->capabilities &= ~BDI_CAP_STRICTLIMIT;
+		break;
+	case 1:
+		bdi->capabilities |= BDI_CAP_STRICTLIMIT;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return count;
+}
+static ssize_t strictlimit_show(struct device *dev,
+		struct device_attribute *attr, char *page)
+{
+	struct backing_dev_info *bdi = dev_get_drvdata(dev);
+
+	return snprintf(page, PAGE_SIZE-1, "%d\n",
+			!!(bdi->capabilities & BDI_CAP_STRICTLIMIT));
+}
+static DEVICE_ATTR_RW(strictlimit);
+
 static struct attribute *bdi_dev_attrs[] = {
 	&dev_attr_read_ahead_kb.attr,
 	&dev_attr_min_ratio.attr,
 	&dev_attr_max_ratio.attr,
 	&dev_attr_stable_pages_required.attr,
+	&dev_attr_strictlimit.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(bdi_dev);

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/