Subject:[PATCH 1:1] boot paramer "root=" gets a list of devices

From: Raz Ben Yehuda
Date: Thu Dec 15 2011 - 04:23:17 EST


From: Raz ben yehuda <rbenyehuda@xxxxxxxx>

Patch is aimed to bypass the need for initramfs when it is not
known which disk has the root file system.

Example: The kernel boot parameter "root=/dev/sda1,/dev/sdc1,/dev/sdb4".
Check if /dev/sda1 exists ,if /dev/sda1 does not exist then try
/dev/sdc1 an so on upto the first a device that exists ( ROOT_DEV != 0 ),
else use the last device as the mount device.

Signed-off-by: Raz Ben Yehuda <rbenyehuda@xxxxxxxx>

---

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 0f6e1d9..02ed235 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -162,9 +162,10 @@ done:
* of partition - device number of disk plus the partition number
* 5) /dev/<disk_name>p<decimal> - same as the above, that form is
* used when disk name of partitioned disk ends on a digit.
- * 6) PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF representing the
+ * 6) /dev/<disk name><decimal>,/dev/<disk name><decimal>,...
+ * 7) PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF representing the
* unique id of a partition if the partition table provides it.
- * 7) PARTUUID=<UUID>/PARTNROFF=<int> to select a partition in relation to
+ * 8) PARTUUID=<UUID>/PARTNROFF=<int> to select a partition in relation to
* a partition with a known unique id.
*
* If name doesn't have fall into the categories above, we return (0,0).
@@ -469,6 +470,63 @@ void __init mount_root(void)
#endif
}

+void scan_root_dev_list(void)
+{
+ char *root_device_eol;
+ char *tmp_dev_name = saved_root_name;
+ char *comma;
+
+ comma = root_device_name;
+ root_device_eol = root_device_name + strlen(root_device_name);
+
+ for (; comma != root_device_eol ;) {
+ char dev_name[64];
+ /*
+ * scan for active device from
+ * root=/dev/sda1,/dev/sda2,...
+ */
+ comma = strchr(tmp_dev_name, ',');
+ if (!comma) {
+ /*
+ * if there is no list of devices
+ * ( root=/dev/sdaX) or we are at the end
+ */
+ root_device_name = tmp_dev_name;
+ ROOT_DEV = name_to_dev_t(root_device_name);
+ printk(KERN_INFO "trying device %s\n",
+ root_device_name);
+ break;
+ }
+ /*
+ * ok, we failed with first device,
+ * move to next one in the comma separated list
+ */
+ memset(dev_name, 0, sizeof(dev_name));
+ strncpy(dev_name, tmp_dev_name,
+ (long)comma - (long)tmp_dev_name);
+ ROOT_DEV = name_to_dev_t(dev_name);
+ printk(KERN_INFO "trying device %s\n", dev_name);
+ if (ROOT_DEV == 0) {
+ tmp_dev_name = comma + 1;
+ if (tmp_dev_name < root_device_eol)
+ continue;
+ break;
+ }
+ /*
+ * we're lucky, we have a device,
+ * let set root_device_name to point at it
+ */
+ strcpy(root_device_name, dev_name);
+ break;
+ }
+ if (ROOT_DEV == 0) {
+ printk(KERN_INFO "kernel is likely to panic aiee..\n");
+ return;
+ }
+ printk(KERN_INFO "Found %s appropriate for boot\n",
+ root_device_name);
+}
+
/*
* Prepare the namespace - decide what/where to mount, load ramdisks, etc.
*/
@@ -500,10 +558,10 @@ void __init prepare_namespace(void)
mount_block_root(root_device_name, root_mountflags);
goto out;
}
- ROOT_DEV = name_to_dev_t(root_device_name);
- if (strncmp(root_device_name, "/dev/", 5) == 0)
- root_device_name += 5;
+ scan_root_dev_list();
}
+ if (strncmp(root_device_name, "/dev/", 5) == 0)
+ root_device_name += 5;

if (initrd_load())
goto out;


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