Re: rootdelay

From: David N. Welton
Date: Mon Apr 25 2005 - 16:45:21 EST

William Park <opengeometry@xxxxxxxx> writes:

> > > > was wondering if there were any interest in my own efforts in that
> > > > direction:
> >
> > > > http://dedasys.com/freesoftware/patches/blkdev_wakeup.patch which

...

> > Thanks! I don't wish to be a pest, but not having heard a "no",
> > I'll send another ping out. Perhaps a simple description is
> > better than the patch for busy people:

> > In init/do_mounts.c, mount_root does an interruptible_sleep_on
> > a wait queue, and goes on about its business after
> > register_blkdev in drivers/block/genhd.c does a
> > wake_up_interruptible on it, so that mounting the root device
> > happens exactly when it needs to, no sooner, no later, and
> > doesn't depend on any fiddly timing issues.

> Post your patch to the list, and I'll get it from a newsgroup.

I sent the URL to the patch so as to avoid sending it around, but
since I don't know the etiquette of this list, I will attach the patch
for your perusal.

Thankyou once again,
--
David N. Welton
- http://www.dedasys.com/davidw/

Apache, Linux, Tcl Consulting
- http://www.dedasys.com/

diff -ur -X dontdiff /usr/local/src/linux/arch/i386/kernel/reboot.c kernel/arch/i386/kernel/reboot.c
Only in /usr/local/src/linux/: config-2.6.5-1-686
Only in kernel/: do_mounts.patch
diff -ur -X dontdiff /usr/local/src/linux/drivers/block/genhd.c kernel/drivers/block/genhd.c
--- /usr/local/src/linux/drivers/block/genhd.c 2004-06-17 11:42:01.000000000 +0200
+++ kernel/drivers/block/genhd.c 2004-07-30 16:19:21.000000000 +0200
@@ -14,9 +14,14 @@
#include <linux/slab.h>
#include <linux/kmod.h>
#include <linux/kobj_map.h>
+#include <linux/wait.h>
+#include <linux/sched.h>

#define MAX_PROBE_HASH 255 /* random */

+DECLARE_WAIT_QUEUE_HEAD(disk_wait_h);
+EXPORT_SYMBOL(disk_wait_h);
+
static struct subsystem block_subsys;

/*
@@ -57,6 +62,47 @@
return len;
}

+/*
+ *-----------------------------------------------------------------------------
+ *
+ * get_blkdevs --
+ *
+ * Returns an array of all the block device names.
+ *
+ *-----------------------------------------------------------------------------
+ */
+
+char **get_blkdevs(void)
+{
+ int i = 0;
+ int len = 0;
+ struct list_head *p;
+ char **names = NULL;
+ struct gendisk *sgp;
+ char buf[BDEVNAME_SIZE];
+
+ down_read(&block_subsys.rwsem);
+
+ list_for_each(p, &block_subsys.kset.list) {
+ len ++;
+ }
+
+ names = kmalloc(sizeof(char *) * len + 1, GFP_KERNEL);
+
+ list_for_each(p, &block_subsys.kset.list) {
+ sgp = list_entry(p, struct gendisk, kobj.entry);
+ names[i] = kmalloc(strlen(disk_name(sgp, 0, buf)), GFP_KERNEL);
+ strcpy(names[i], disk_name(sgp, 0, buf));
+ i ++;
+ }
+ names[i] = NULL;
+ up_read(&block_subsys.rwsem);
+
+ return names;
+}
+
+EXPORT_SYMBOL(get_blkdevs);
+
int register_blkdev(unsigned int major, const char *name)
{
struct blk_major_name **n, *p;
@@ -197,6 +243,11 @@
disk->minors, NULL, exact_match, exact_lock, disk);
register_disk(disk);
blk_register_queue(disk);
+
+ /* Wake up queue in init/main.c. */
+ printk("Waking up queue on %s\n",
+ disk->disk_name);
+ wake_up_interruptible(&disk_wait_h);
}

EXPORT_SYMBOL(add_disk);
diff -ur -X dontdiff /usr/local/src/linux/drivers/isdn/hardware/mISDN/hfc_multi.c kernel/drivers/isdn/hardware/mISDN/hfc_multi.c
Only in kernel/drivers/scsi: #sd.c#
diff -ur -X dontdiff /usr/local/src/linux/drivers/scsi/sd.c kernel/drivers/scsi/sd.c
diff -ur -X dontdiff /usr/local/src/linux/drivers/usb/storage/usb.c kernel/drivers/usb/storage/usb.c
diff -ur -X dontdiff /usr/local/src/linux/include/asm-i386/mach-default/mach_reboot.h kernel/include/asm-i386/mach-default/mach_reboot.h
Only in kernel/include/linux: #list.h#
diff -ur -X dontdiff /usr/local/src/linux/include/linux/genhd.h kernel/include/linux/genhd.h
--- /usr/local/src/linux/include/linux/genhd.h 2004-04-26 15:08:54.000000000 +0200
+++ kernel/include/linux/genhd.h 2004-07-30 16:29:45.000000000 +0200
@@ -16,6 +16,10 @@
#include <linux/smp.h>
#include <linux/string.h>
#include <linux/fs.h>
+#include <linux/wait.h>
+
+/* Wait queue to wait on disks coming online. */
+extern wait_queue_head_t disk_wait_h;

enum {
/* These three have identical behaviour; use the second one if DOS FDISK gets
@@ -191,6 +195,7 @@

extern void set_device_ro(struct block_device *bdev, int flag);
extern void set_disk_ro(struct gendisk *disk, int flag);
+extern char **get_blkdevs(void);

/* drivers/char/random.c */
extern void add_disk_randomness(struct gendisk *disk);
diff -ur -X dontdiff /usr/local/src/linux/init/do_mounts.c kernel/init/do_mounts.c
--- /usr/local/src/linux/init/do_mounts.c 2004-05-19 10:22:22.000000000 +0200
+++ kernel/init/do_mounts.c 2004-07-30 16:32:26.000000000 +0200
@@ -11,6 +11,8 @@
#include <linux/nfs_fs_sb.h>
#include <linux/nfs_mount.h>

+#include <linux/genhd.h>
+
#include "do_mounts.h"

extern int get_filesystem_list(char * buf);
@@ -350,8 +360,41 @@
}
#endif

+/*
+ *-----------------------------------------------------------------------------
+ *
+ * match_root_name --
+ *
+ * Returns 1 if the root_device_name appears amongst the list of
+ * block devices, 0 otherwise.
+ *
+ *-----------------------------------------------------------------------------
+ */
+
+static int __init match_root_name(void) {
+ char **names = NULL;
+ int i = 0;
+ int match = 0;
+
+ names = get_blkdevs();
+ while (names[i] != NULL) {
+ if (match == 0 && strncmp(names[i],
+ root_device_name,
+ strlen(names[i])) == 0) {
+ match = 1;
+ printk("Block device %s matches %s root_device_name, continuing\n",
+ names[i], root_device_name);
+ }
+ kfree(names[i]);
+ i ++;
+ }
+ kfree(names);
+ return match;
+}
+
void __init mount_root(void)
{
+
#ifdef CONFIG_ROOT_NFS
if (MAJOR(ROOT_DEV) == UNNAMED_MAJOR) {
if (mount_nfs_root())
@@ -373,6 +416,14 @@
change_floppy("root floppy");
}
#endif
+
+ /* Here, we wait for the root device to show up, or if it's
+ * already there, we just go on. */
+ while (match_root_name() == 0) {
+ printk("Waiting for root device to wake us up\n");
+ interruptible_sleep_on(&disk_wait_h);
+ }
+
create_dev("/dev/root", ROOT_DEV, root_device_name);
mount_block_root("/dev/root", root_mountflags);
}
diff -ur -X dontdiff /usr/local/src/linux/init/main.c kernel/init/main.c
--- /usr/local/src/linux/init/main.c 2004-06-17 11:42:42.000000000 +0200
+++ kernel/init/main.c 2004-07-30 11:43:48.000000000 +0200
@@ -44,6 +44,11 @@
#include <linux/unistd.h>
#include <linux/rmap.h>

+#include <linux/genhd.h>
+#include <linux/wait.h>
+#include <linux/sched.h>
+
+
#include <asm/io.h>
#include <asm/bugs.h>

diff -ur -X dontdiff /usr/local/src/linux/kernel/printk.c kernel/kernel/printk.c
diff -ur -X dontdiff /usr/local/src/linux/kernel/sys.c kernel/kernel/sys.c