[LTP] [PATCH 1/2] tst_find_backing_dev: Get dev name from /sys/dev/block/*/uevent

[Alessandro Carminati]

In some minimal Linux the /dev/root can be missing. The consequence for this
is that mountinfo doesn't contain the correct information.

The unevent file in sysfs is another method to retrieve device info given 
a major/minor.

btrfs subvolumes can be an exception to this rule, but they are not expected
to be used in the current usecase.

This solution requires sysfs to be mounted in /sys, but considering many 
tests depends on the same, including the ioctl_loop05 that triggered this 
patch, this requirement is not too restricted, and the old mountinfo can be 
dropped altogether.

$ sudo /usr/lib/ltp-testsuite/testcases/bin/ioctl_loop05
tst_test.c:1363: TINFO: Timeout per run is 0h 05m 00s
tst_test.c:1115: TINFO: ext2/ext3/ext4 is supported by the test
tst_device.c:91: TINFO: Found free device 0 '/dev/loop0'
loop0: detected capacity change from 0 to 2048
tst_device.c:570: TINFO: Device name retrived through mountinfo
ioctl_loop05.c:126: TINFO: backing dev(/dev/root) logical_block_size is 512
ioctl_loop05.c:62: TINFO: Without setting lo_offset or sizelimit
ioctl_loop05.c:45: TINFO: In dio mode
ioctl_loop05.c:48: TPASS: lo_flags has LO_FLAGS_DIRECT_IO flag
ioctl_loop05.c:52: TBROK: Failed to open FILE '/sys/block/loop0/loop/dio' for reading: ENOENT (2)

Summary:
passed   1
failed   0
broken   1
skipped  0
warnings 0

The example here shows what happen if sysfs is not mounted and the
mountinfo method is used: the tests that depends on sysfs fail with
broken and not just warn.

Signed-off-by: Richard Palethorpe <rpalethorpe@suse.com>
Signed-off-by: Alessandro Carminati <alessandro.carminati@gmail.com>
---
 lib/tst_device.c | 41 ++++++++++-------------------------------
 1 file changed, 10 insertions(+), 31 deletions(-)

diff --git a/lib/tst_device.c b/lib/tst_device.c
index 8419b80c3..4ccb71ac8 100644
--- a/lib/tst_device.c
+++ b/lib/tst_device.c
@@ -520,48 +520,27 @@ void tst_find_backing_dev(const char *path, char *dev)
 {
 	struct stat buf;
 	FILE *file;
-	char line[PATH_MAX];
-	char *pre = NULL;
-	char *next = NULL;
-	unsigned int dev_major, dev_minor, line_mjr, line_mnr;
-	unsigned int len, best_match_len = 1;
-	char mnt_point[PATH_MAX];
+	unsigned int dev_major, dev_minor;
+	char uevent_path[PATH_MAX];
+	char dev_name[NAME_MAX];
 
 	if (stat(path, &buf) < 0)
 		tst_brkm(TWARN | TERRNO, NULL, "stat() failed");
 
+	*dev = '\0';
 	dev_major = major(buf.st_dev);
 	dev_minor = minor(buf.st_dev);
-	file = SAFE_FOPEN(NULL, "/proc/self/mountinfo", "r");
-	*dev = '\0';
-
-	while (fgets(line, sizeof(line), file)) {
-		if (sscanf(line, "%*d %*d %d:%d %*s %s",
-			&line_mjr, &line_mnr, mnt_point) != 3)
-			continue;
 
-		pre = strstr(line, " - ");
-		pre = strtok_r(pre, " ", &next);
-		pre = strtok_r(NULL, " ", &next);
-		pre = strtok_r(NULL, " ", &next);
+	sprintf(uevent_path,
+		"/sys/dev/block/%d:%d/uevent", dev_major, dev_minor);
 
-		if (line_mjr == dev_major && line_mnr == dev_minor) {
-			strcpy(dev, pre);
-			break;
-		}
+	if (!access(uevent_path, R_OK)) {
+		FILE_LINES_SCANF(NULL, uevent_path, "DEVNAME=%s", dev_name);
 
-		len = count_match_len(path, mnt_point);
-		if (len > best_match_len) {
-			strcpy(dev, pre);
-			best_match_len = len;
-		}
+		if (dev_name[0])
+			sprintf(dev, "/dev/%s", dev_name);
 	}
 
-	SAFE_FCLOSE(NULL, file);
-
-	if (!*dev)
-		tst_brkm(TBROK, NULL, "Cannot find block device for %s", path);
-
 	if (stat(dev, &buf) < 0)
 		tst_brkm(TWARN | TERRNO, NULL, "stat(%s) failed", dev);
 
-- 
2.34.1