[dm-devel] [PATCH v3 5/5] libmultipath: limit reading 0xc9 vpd page

[Benjamin Marzinski]

Only rdac arrays support 0xC9 vpd page inquiries. All other arrays will
return a failure. Only do the rdac inquiry when detecting array
capabilities if the array's path checker is explicitly set to rdac, or
the path checker is not set, and the array reports that it supports vpd
page 0xC9 in the Supported VPD Pages (0x00) vpd page.

Multipath was doing the check if either the path checker was set to
rdac, or no path checker was set.  This means that for almost all
non-rdac arrays, multipath was issuing a bad inquiry. This was annoying
users.

Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
---
 libmultipath/discovery.c | 17 +++++++++++++++++
 libmultipath/discovery.h |  1 +
 libmultipath/propsel.c   | 10 ++++++----
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/libmultipath/discovery.c b/libmultipath/discovery.c
index f901e9ff..e818585a 100644
--- a/libmultipath/discovery.c
+++ b/libmultipath/discovery.c
@@ -1348,6 +1348,23 @@ fetch_vpd_page(int fd, int pg, unsigned char *buff, int maxlen)
 	return buff_len;
 }
 
+/* based on sg_inq.c from sg3_utils */
+bool
+is_vpd_page_supported(int fd, int pg)
+{
+	int i, len;
+	unsigned char buff[4096];
+
+	len = fetch_vpd_page(fd, 0x00, buff, sizeof(buff));
+	if (len < 0)
+		return false;
+
+	for (i = 4; i < len; ++i)
+		if (buff[i] == pg)
+			return true;
+	return false;
+}
+
 int
 get_vpd_sgio (int fd, int pg, int vend_id, char * str, int maxlen)
 {
diff --git a/libmultipath/discovery.h b/libmultipath/discovery.h
index 6444887d..d3193daf 100644
--- a/libmultipath/discovery.h
+++ b/libmultipath/discovery.h
@@ -56,6 +56,7 @@ int sysfs_get_asymmetric_access_state(struct path *pp,
 				      char *buff, int buflen);
 int get_uid(struct path * pp, int path_state, struct udev_device *udev,
 	    int allow_fallback);
+bool is_vpd_page_supported(int fd, int pg);
 
 /*
  * discovery bitmask
diff --git a/libmultipath/propsel.c b/libmultipath/propsel.c
index fa4ac5d9..f771a830 100644
--- a/libmultipath/propsel.c
+++ b/libmultipath/propsel.c
@@ -496,13 +496,15 @@ check_rdac(struct path * pp)
 {
 	int len;
 	char buff[44];
-	const char *checker_name;
+	const char *checker_name = NULL;
 
 	if (pp->bus != SYSFS_BUS_SCSI)
 		return 0;
-	/* Avoid ioctl if this is likely not an RDAC array */
-	if (__do_set_from_hwe(checker_name, pp, checker_name) &&
-	    strcmp(checker_name, RDAC))
+	/* Avoid checking 0xc9 if this is likely not an RDAC array */
+	if (!__do_set_from_hwe(checker_name, pp, checker_name) &&
+	    !is_vpd_page_supported(pp->fd, 0xC9))
+		return 0;
+	if (checker_name && strcmp(checker_name, RDAC))
 		return 0;
 	len = get_vpd_sgio(pp->fd, 0xC9, 0, buff, 44);
 	if (len <= 0)
-- 
2.17.2