From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Benjamin Marzinski <bmarzins@redhat.com>

Date: Mon, 15 Nov 2021 10:54:35 -0600

Subject: [PATCH] multipathd: avoid unnecessary path read-only reloads

A mulitpath device can only be reloaded read/write when all paths are

read/write. Also, whenever a read-only device is rescanned, the scsi

subsystem will first unconditionally issue a uevent with DISK_RO=0

before checking the read-only status, and if it the device is still

read-only, issuing another uevent with DISK_RO=1. These uevents cause

pointless reloads when read-only paths are rescanned. To avoid this,

check to see if all paths are read/write before changing a multipath

device from read-only to read/write.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>

---

 libmultipath/sysfs.c | 22 ++++++++++++++++++++++

 libmultipath/sysfs.h |  1 +

 multipathd/main.c    | 31 ++++++++++++++++++++++++++++++-

 3 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/libmultipath/sysfs.c b/libmultipath/sysfs.c

index 62ec2ed7..a57bd60e 100644

--- a/libmultipath/sysfs.c

+++ b/libmultipath/sysfs.c

@@ -236,6 +236,28 @@ sysfs_get_size (struct path *pp, unsigned long long * size)

 	return 0;

 }

+int

+sysfs_get_ro (struct path *pp)

+{

+	int ro;

+	char buff[3]; /* Either "0\n\0" or "1\n\0" */

+

+	if (!pp->udev)

+		return -1;

+

+	if (sysfs_attr_get_value(pp->udev, "ro", buff, sizeof(buff)) <= 0) {

+		condlog(3, "%s: Cannot read ro attribute in sysfs", pp->dev);

+		return -1;

+	}

+

+	if (sscanf(buff, "%d\n", &ro) != 1 || ro < 0 || ro > 1) {

+		condlog(3, "%s: Cannot parse ro attribute", pp->dev);

+		return -1;

+	}

+

+	return ro;

+}

+

 int sysfs_check_holders(char * check_devt, char * new_devt)

 {

 	unsigned int major, new_minor, table_minor;

diff --git a/libmultipath/sysfs.h b/libmultipath/sysfs.h

index 9ae30b39..91092e44 100644

--- a/libmultipath/sysfs.h

+++ b/libmultipath/sysfs.h

@@ -13,6 +13,7 @@ ssize_t sysfs_attr_get_value(struct udev_device *dev, const char *attr_name,

 ssize_t sysfs_bin_attr_get_value(struct udev_device *dev, const char *attr_name,

 				 unsigned char * value, size_t value_len);

 int sysfs_get_size (struct path *pp, unsigned long long * size);

+int sysfs_get_ro(struct path *pp);

 int sysfs_check_holders(char * check_devt, char * new_devt);

 bool sysfs_is_multipathed(const struct path *pp);

 #endif

diff --git a/multipathd/main.c b/multipathd/main.c

index 823b53a2..e2b9d546 100644

--- a/multipathd/main.c

+++ b/multipathd/main.c

@@ -1256,6 +1256,35 @@ fail:

 	return PATH_REMOVE_FAILED;

 }

+static bool

+needs_ro_update(struct multipath *mpp, int ro)

+{

+	struct pathgroup * pgp;

+	struct path * pp;

+	unsigned int i, j;

+	struct dm_info *dmi = NULL;

+

+	if (!mpp || ro < 0)

+		return false;

+	dm_get_info(mpp->alias, &dmi);

+	if (!dmi) /* assume we do need to reload the device */

+		return true;

+	if (dmi->read_only == ro) {

+		free(dmi);

+		return false;

+	}

+	free(dmi);

+	if (ro == 1)

+		return true;

+	vector_foreach_slot (mpp->pg, pgp, i) {

+		vector_foreach_slot (pgp->paths, pp, j) {

+			if (sysfs_get_ro(pp) == 1)

+				return false;

+		}

+	}

+	return true;

+}

+

 static int

 uev_update_path (struct uevent *uev, struct vectors * vecs)

 {

@@ -1321,7 +1350,7 @@ uev_update_path (struct uevent *uev, struct vectors * vecs)

 		}

 		ro = uevent_get_disk_ro(uev);

-		if (mpp && ro >= 0) {

+		if (needs_ro_update(mpp, ro)) {

 			condlog(2, "%s: update path write_protect to '%d' (uevent)", uev->kernel, ro);

 			if (mpp->wait_for_udev)