[BusyBox] find_root_device

Larry Doolittle ldoolitt at recycle.lbl.gov
Tue May 22 15:53:21 UTC 2001


Without the following patch, df and mount show (null) for the
root device on my 2.0.36 workstation.  With this patch, they
correctly find /dev/sda1.  The problem is that stat("/",..)
returns st_dev=(8,1), but st_rdev=(0,0).  If you tell me
that 2.0.36 is broken, I'll only half believe you.  My
uptime is well over six months.

I added more diagnostic detail, and put in a fallback mode
that may be more useful than (null).

I don't fully understand the difference between st_dev and
st_rdev, but I think this patch is correct anyway.  :*)

      - Larry

--- /home/ldoolitt/cvs/busybox/libbb/find_root_device.c	Tue May 15 12:32:17 2001
+++ find_root_device.c	Tue May 22 14:43:25 2001
@@ -39,16 +39,18 @@
 	struct dirent *entry;
 	struct stat statBuf, rootStat;
 	char *fileName;
+	dev_t dev;
 
 	if (stat("/", &rootStat) != 0) {
-		error_msg("could not stat '/'");
+		perror_msg("could not stat '/'");
 		return NULL;
 	}
+	if ((dev = rootStat.st_rdev)==0) dev=rootStat.st_dev;
 
 	dir = opendir("/dev");
 	if (!dir) {
-		error_msg("could not open '/dev'");
-		return NULL;
+		perror_msg("could not open '/dev'");
+		goto fallback;
 	}
 
 	while((entry = readdir(dir)) != NULL) {
@@ -64,14 +66,18 @@
 		 * devices, so make sure this is a block device */
 		if (stat(fileName, &statBuf) == 0 && 
 				S_ISBLK(statBuf.st_mode)!=0 &&
-				statBuf.st_rdev == rootStat.st_rdev) {
+				statBuf.st_rdev == dev) {
 			return fileName; 
 		}
 		free(fileName);
 	}
 	closedir(dir);
 
-	return NULL;
+fallback:
+	/* don't use stack space, caller expects to free() result */
+	fileName=xmalloc(20);
+	sprintf(fileName,"(rdev %u)",(unsigned int) rootStat.st_rdev);
+	return fileName;
 }
 
 





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