2493 change efi_rescan() to wait longer

Change efi_rescan() to loop 10 times instead of 5 on EBUSY and
to sleep at the end of each loop. This helps with some instances
where the kernel does not reload the partition table fast enough
for ZFS to detect.

Signed-off-by: Andrew Hamilton <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes openzfs#2493

Author: Andrew Hamilton

lib/libefi/rdwr_efi.c

@@ -506,16 +506,17 @@ int
 efi_rescan(int fd)
 {
 #if defined(__linux__)
-	int retry = 5;
+	int retry = 10;
 	int error;
 
 	/* Notify the kernel a devices partition table has been updated */
 	while ((error = ioctl(fd, BLKRRPART)) != 0) {
-		if (--retry == 0) {
+		if ((--retry == 0) || (errno != EBUSY)) {
 			(void) fprintf(stderr, "the kernel failed to rescan "
 			    "the partition table: %d\n", errno);
 			return (-1);
 		}
+		usleep(50000);
 	}
 #endif