Re: [patch 1/1] md: Software Raid autodetect dev list not array

Neil Brown
2007-08-24T03:37:49Z

On Wednesday August 22, mjevans1983@comcast.net wrote:
> From: Michael J. Evans <mjevans1983@gmail.com>
>
> In current release kernels the md module (Software RAID) uses a static array
> (dev_t[128]) to store partition/device info temporarily for autostart.
>
> This patch replaces that static array with a list.

I must admit that I'm not very keen on this.
I would much rather that in-kernel autodetect were deprecated rather
than enhanced.

Just use 'mdadm' in an initrd, or during normal boot, to assemble all
your arrays.

However.....

> =============================================================
> --- linux/drivers/md/md.c.orig 2007-08-21 03:19:42.511576248 -0700
> +++ linux/drivers/md/md.c 2007-08-21 04:30:09.775525710 -0700
> @@ -24,4 +24,6 @@
>
> + - autodetect dev list not array: Michael J. Evans <mjevans1983@gmail.com>
> +
> This program is free software; you can redistribute it and/or modify
> it under the terms of the GNU General Public License as published by
> the Free Software Foundation; either version 2, or (at your option)
> @@ -5752,13 +5754,25 @@ void md_autodetect_dev(dev_t dev)
> * Searches all registered partitions for autorun RAID arrays
> * at boot time.
> */
> -static dev_t detected_devices[128];
> -static int dev_cnt;
> +
> +static LIST_HEAD(all_detected_devices);
> +/* FIXME : Should these 4 lines instead go in to include/linux/raid/md_k.h ?

No. No-one outside this file uses them, so they are fine where they
are.

> */
> +struct detected_devices_node {
> + struct list_head list;
> + dev_t dev;
> +};
>
> void md_autodetect_dev(dev_t dev)
> {
> - if (dev_cnt >= 0 && dev_cnt < 127)
> - detected_devices[dev_cnt++] = dev;
> + struct detected_devices_node *node_detected_dev;
> + node_detected_dev = kzalloc(sizeof(*node_detected_dev), GFP_KERNEL);\
> + if (node_detected_dev) {
> + node_detected_dev->dev = dev;
> + list_add(&node_detected_dev->list, &all_detected_devices);

Probably list_add_tail would be better so the ordering is the same as
it was before?

> + } else {
> + printk(KERN_CRIT "md: kzAlloc node failed, skipping device."
> + " : 0x%p.\n", node_detected_dev);
> + }

> }
>
>
> @@ -5765,7 +5779,13 @@ static void autostart_arrays(int part)
> static void autostart_arrays(int part)
> {
> mdk_rdev_t *rdev;
> - int i;
> + struct detected_devices_node *node_detected_dev;
> + dev_t dev;
> + int i_scanned, i_passed, i_loops;
> + signed int i_found;
> + i_scanned = 0;
> + i_passed = 0;
> + i_loops = 0;

i_passed is never used.

And what is the point of i_loops (and i_scanned)? The comments
at the top of the patch should explain this if there is a good reason.

>
> printk(KERN_INFO "md: Autodetecting RAID arrays.\n");
>
> @@ -5772,3 +5792,11 @@ static void autostart_arrays(int part)
> - for (i = 0; i < dev_cnt; i++) {
> - dev_t dev = detected_devices[i];
> -
> + /* FIXME: max 'int' #DEFINEd somewhere? not 0x7FFFFFFF ? */
> + while (!list_empty(&all_detected_devices) && i_loops < 0x7FFFFFFF) {
> + i_scanned++;
> + node_detected_dev = NULL;
> + node_detected_dev = list_entry(all_detected_devices.next,
> + struct detected_devices_node, list);
> + if (node_detected_dev) {

list_entry will *never* return NULL. It simply doesn't pointer
arithmetic. (Well, I guess it could return NULL if it was passed
NULL, and the struct-offset were 0, but that isn't the case here).

So you don't need this 'if' at all.

> + list_del(&node_detected_dev->list);
> + dev = node_detected_dev->dev;
> + kfree(node_detected_dev);
> + /* Indent is now off by one, but the old code is after this. */

so you don't need to worrying about indents.

> @@ -5781,8 +5809,16 @@ static void autostart_arrays(int part)
> continue;
> }
> list_add(&rdev->same_set, &pending_raid_disks);
> + /* Indent is now off by one, but the old code is above this. */
> +
> + } else {
> + printk(KERN_CRIT "md: Invalid list node, skipping.\n");
> + }
> + i_loops++;
> }
> - dev_cnt = 0;
> +
> + printk(KERN_INFO "md: Passes %d : Scanned %d and added %d devices.\n",
> + i_loops, i_scanned, i_passed);
>
> autorun_devices(part);
> }

I'm not dead-set against the change, and if you tidy it up I'll
probably accept it, but I really think you would be better off skipping
the in-kernel autodetect stuff altogether and use mdadm to assemble
your arrays.

NeilBrown