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

Alessandro Carminati alessandro.carminati@gmail.com
Wed Nov 2 21:34:12 CET 2022


In some minimal Linux, the /dev/root can be missing. The consequence of
this is that mountinfo doesn't contain the correct information. btrfs
file systems are yet another point of trouble for this function.

The unevent file in sysfs is another method to retrieve device info
using the sysfs.

btrfs file systems are special from the device name retrieval, and in
place of use of the minor/major they are approached by using the uuid.
In the end, btrfs strategy is a slightly modified version of the same
unevent strategy.

Non btrfs look in "/sys/dev/block/%d:%d/uevent" major, minor
btrfs look in /sys/fs/btrfs/%s/devices/%s/uevent, uuid, devname

The btrfs handling requires BTRFS specific ioctl for finding the
file system uuid, and for this reason, btrfs/ioctl.h is needed.

Signed-off-by: Richard Palethorpe <rpalethorpe@suse.com>
Signed-off-by: Alessandro Carminati <alessandro.carminati@gmail.com>
---
 lib/tst_device.c | 86 ++++++++++++++++++++++++++++++++----------------
 1 file changed, 57 insertions(+), 29 deletions(-)

diff --git a/lib/tst_device.c b/lib/tst_device.c
index 8419b80c3..4c2bde846 100644
--- a/lib/tst_device.c
+++ b/lib/tst_device.c
@@ -33,6 +33,8 @@
 #include <stdint.h>
 #include <inttypes.h>
 #include <sys/sysmacros.h>
+#include <btrfs/ioctl.h>
+#include <dirent.h>
 #include "lapi/syscalls.h"
 #include "test.h"
 #include "safe_macros.h"
@@ -45,6 +47,7 @@
 
 #define DEV_FILE "test_dev.img"
 #define DEV_SIZE_MB 300u
+#define UUID_STR_SZ 37
 
 static char dev_path[1024];
 static int device_acquired;
@@ -519,48 +522,73 @@ static int count_match_len(const char *first, const char *second)
 void tst_find_backing_dev(const char *path, char *dev)
 {
 	struct stat buf;
+	struct btrfs_ioctl_fs_info_args args = {0};
+	struct dirent *d;
 	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];
+	char uevent_path[PATH_MAX];
+	char dev_name[NAME_MAX];
+	char bdev_path[PATH_MAX];
+	char btrfs_uuid_str[UUID_STR_SZ];
+	DIR *dir;
+	unsigned int dev_major, dev_minor;
+	int fd;
 
 	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);
 
-		if (line_mjr == dev_major && line_mnr == dev_minor) {
-			strcpy(dev, pre);
-			break;
+	if (dev_major == 0) {
+		tst_resm(TINFO, "Use BTRFS specific strategy");
+		dir = opendir("/");
+		fd = dirfd(dir);
+		if (!ioctl(fd, BTRFS_IOC_FS_INFO, &args)) {
+			sprintf(btrfs_uuid_str,
+				"%02x%02x%02x%02x-%02x%02x-"
+				"%02x%02x-%02x%02x-"
+				"%02x%02x%02x%02x%02x%02x",
+				args.fsid[0],args.fsid[1],
+				args.fsid[2],args.fsid[3],
+				args.fsid[4],args.fsid[5],
+				args.fsid[6],args.fsid[7],
+				args.fsid[8],args.fsid[9],
+				args.fsid[10],args.fsid[11],
+				args.fsid[12],args.fsid[13],
+				args.fsid[14],args.fsid[15]);
+			sprintf(bdev_path,
+				"/sys/fs/btrfs/%s/devices", btrfs_uuid_str);
 		}
-
-		len = count_match_len(path, mnt_point);
-		if (len > best_match_len) {
-			strcpy(dev, pre);
-			best_match_len = len;
+		closedir(dir);
+		dir = opendir(bdev_path);
+		if (!dir){
+			tst_brkm(TWARN | TERRNO, NULL,
+				"can't opendir %d", dir);
+		}
+		while (d = readdir(dir)){
+			if (d->d_name[0]!='.')
+				break;
+		}
+		uevent_path[0]='\0';
+		closedir(dir);
+		if (d!=NULL) {
+			sprintf(uevent_path, "%s/%s/uevent",
+				bdev_path, d->d_name);
 		}
+	} else {
+
+		tst_resm(TINFO, "Use uevent strategy");
+		sprintf(uevent_path,
+			"/sys/dev/block/%d:%d/uevent", dev_major, dev_minor);
 	}
 
-	SAFE_FCLOSE(NULL, file);
+	if (!access(uevent_path, R_OK)) {
+		FILE_LINES_SCANF(NULL, uevent_path, "DEVNAME=%s", dev_name);
 
-	if (!*dev)
-		tst_brkm(TBROK, NULL, "Cannot find block device for %s", path);
+		if (dev_name[0])
+			sprintf(dev, "/dev/%s", dev_name);
+	}
 
 	if (stat(dev, &buf) < 0)
 		tst_brkm(TWARN | TERRNO, NULL, "stat(%s) failed", dev);
-- 
2.34.1



More information about the ltp mailing list