Re: pvgrub2 and old grub menu.lst

[Andrey Borzenkov <arvidjaar@gmail.com>]

В Wed, 2 Apr 2014 14:29:50 +0400
Andrey Borzenkov <arvidjaar@gmail.com> пишет:

> On Wed, Apr 2, 2014 at 12:43 PM, Michael Chang <mchang@suse.com> wrote:
> > On Tue, Apr 01, 2014 at 08:06:44PM +0400, Andrey Borzenkov wrote:
> >> В Tue, 1 Apr 2014 15:46:22 +0800
> >> Michael Chang <mchang@suse.com> пишет:
> >>
> >> > While trying to boot xen pv guest with old grub config (menu.lst),
> >> > the pvgrub2 loads it's menu successfully, but when you attemp to boot
> >> > the kernel it failed with the following message.
> >> >
> >> >   error: couldn't load file /boot/vmlinuz-3.0.76-0.11-xen.
> >> >   error: you need to load the kernel first.
> >> >
> >> >   Press any key to continue..."
> >> >
> >> > The kernel is there and boots fine with pygrub.
> >> >
> >> > After some investigation, it boils down to the menu.lst has explicitly
> >> > set it's root device to (hd0,1) and therefore the root device is not
> >> > recognized by pvgrub2.
> >> >
> >> > title Xen -- SUSE Linux Enterprise Server 11 SP3 - 3.0.76-0.11
> >> >   root (hd0,1)
> >> >   kernel /boot/vmlinuz-3.0.76-0.11-xen root=/dev/xvda2 resume=/dev/xvda1
> >> > splash=silent showopts initrd /boot/initrd-3.0.76-0.11.xen
> >> >
> >> > I'd like to know whether old grub configuration is considered or planned
> >> > to work with pvgrub2 ? And is it a viable suggestion to have (hdX,Y) a
> >> > valid xen disk name because it's quite common in some existing configs ?
> >> >
> >>
> >> I believe this technically should work; but this needs someone who
> >> knows how Xen disks is mapped to hd number in legacy grub.
> >>
> >> It would be something like (completely untested)
> >
> > Thank you for the patch. I applied it and tried to test it. The
> > virtdisks[i].handle never matched with num as it's id of the disk (on
> > my system it is 51712).
> >
> 
> As I said, completely untested :)
> 
> > Please pardon my ignorant, can num be the index to the virtdisks array
> > to get the mapped xen disk ?
> >
> 
> pv-grub additionally sorts by handle:
> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=stubdom/grub/mini-os.c;h=9d4bcc76d5f3e9907889948ee0dcea32e19c185b;hb=HEAD#l73
> 
> So to actually map pv-grub hdX we need to do the same.

Could you test patch below (compile-tested)?

From: Andrey Borzenkov <arvidjaar@gmail.com>
Subject: [PATCH] accept also hdX as alias to native Xen disk name

To assign correct disk numbers, sort disks by increasing order of handle
value.  This allows reusing legacy pv-grub menu.lst which is using hdX names.

Suggested-By: Michael Chang <mchang@suse.com>

---
 grub-core/disk/xen/xendisk.c | 45 +++++++++++++++++++++++++++++++++++---------
 1 file changed, 36 insertions(+), 9 deletions(-)

diff --git a/grub-core/disk/xen/xendisk.c b/grub-core/disk/xen/xendisk.c
index 2b11c2a..b18a923 100644
--- a/grub-core/disk/xen/xendisk.c
+++ b/grub-core/disk/xen/xendisk.c
@@ -40,6 +40,7 @@ struct virtdisk
   grub_xen_evtchn_t evtchn;
   void *dma_page;
   grub_xen_grant_t dma_grant;
+  struct virtdisk *compat_next;
 };
 
 #define xen_wmb() mb()
@@ -47,6 +48,7 @@ struct virtdisk
 
 static struct virtdisk *virtdisks;
 static grub_size_t vdiskcnt;
+struct virtdisk *compat_head;
 
 static int
 grub_virtdisk_iterate (grub_disk_dev_iterate_hook_t hook, void *hook_data,
@@ -66,20 +68,32 @@ grub_virtdisk_iterate (grub_disk_dev_iterate_hook_t hook, void *hook_data,
 static grub_err_t
 grub_virtdisk_open (const char *name, grub_disk_t disk)
 {
-  grub_size_t i;
+  int i;
   grub_uint32_t secsize;
   char fdir[200];
   char *buf;
+  int num = -1;
+  struct virtdisk *vd;
 
-  for (i = 0; i < vdiskcnt; i++)
-    if (grub_strcmp (name, virtdisks[i].fullname) == 0)
+  /* For compatibility with pv-grub legacy menu.lst accept hdX as disk name */
+  if (name[0] == 'h' && name[1] == 'd' && name[2])
+    {
+      num = grub_strtoul (name + 2, 0, 10);
+      if (grub_errno)
+	{
+	  grub_errno = 0;
+	  num = -1;
+	}
+    }
+  for (i = 0, vd = compat_head; vd; vd = vd->compat_next, i++)
+    if (i == num || grub_strcmp (name, vd->fullname) == 0)
       break;
-  if (i == vdiskcnt)
+  if (!vd)
     return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "not a virtdisk");
-  disk->data = &virtdisks[i];
-  disk->id = i;
+  disk->data = vd;
+  disk->id = vd - virtdisks;
 
-  grub_snprintf (fdir, sizeof (fdir), "%s/sectors", virtdisks[i].backend_dir);
+  grub_snprintf (fdir, sizeof (fdir), "%s/sectors", vd->backend_dir);
   buf = grub_xenstore_get_file (fdir, NULL);
   if (!buf)
     return grub_errno;
@@ -87,8 +101,7 @@ grub_virtdisk_open (const char *name, grub_disk_t disk)
   if (grub_errno)
     return grub_errno;
 
-  grub_snprintf (fdir, sizeof (fdir), "%s/sector-size",
-		 virtdisks[i].backend_dir);
+  grub_snprintf (fdir, sizeof (fdir), "%s/sector-size", vd->backend_dir);
   buf = grub_xenstore_get_file (fdir, NULL);
   if (!buf)
     return grub_errno;
@@ -264,6 +277,7 @@ fill (const char *dir, void *data)
   grub_err_t err;
   void *buf;
   struct evtchn_alloc_unbound alloc_unbound;
+  struct virtdisk **prev = &compat_head, *vd = compat_head;
 
   /* Shouldn't happen unles some hotplug happened.  */
   if (vdiskcnt >= *ctr)
@@ -374,6 +388,19 @@ fill (const char *dir, void *data)
 
   virtdisks[vdiskcnt].frontend_dir = grub_strdup (fdir);
 
+  /* For compatibility with pv-grub maintain linked list sorted by handle
+     value in increasing order. This allows mapping of (hdX) disk names
+     from legacy menu.lst */
+  while (vd)
+    {
+      if (vd->handle > virtdisks[vdiskcnt].handle)
+	break;
+      prev = &vd->compat_next;
+      vd = vd->compat_next;
+    }
+  virtdisks[vdiskcnt].compat_next = vd;
+  *prev = &virtdisks[vdiskcnt];
+
   vdiskcnt++;
   return 0;
 
-- 
tg: (4afd010..) e/xen/hdX-compat (depends on: master)