Re: [PATCH 2/2] grub2: use stat instead of udevadm for partition lookup

[Michael Chang <mchang@suse.com>]

On Tue, Jul 13, 2021 at 11:25:49AM +0200, Paul Menzel wrote:
> Dear Petr, dear Jeff,
> 
> 
> Am 08.07.21 um 17:55 schrieb Petr Vorel:
> > From: Jeff Mahoney <jeffm@suse.com>
> > 
> > sysfs_partition_path calls udevadm to resolve the sysfs path for
> > a block device. That can be accomplished by stating the device node
> > and using the major/minor to follow the symlinks in /sys/dev/block/.
> > 
> > This cuts the execution time of grub2-mkconfig from 10s to 2s on
> > my system.
> 
> Petr, where you able to reproduce this issue? Could the specifications of
> Jeff’s system be added to the commit message?
> 
> > Signed-off-by: Jeff Mahoney <jeffm@suse.com>
> > [ pvorel: include grub/osdep/major.h ]
> > Signed-off-by: Petr Vorel <pvorel@suse.cz>
> > ---
> >   grub-core/osdep/linux/hostdisk.c | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> > 
> > diff --git a/grub-core/osdep/linux/hostdisk.c b/grub-core/osdep/linux/hostdisk.c
> > index da62f924e..43dc4b0ba 100644
> > --- a/grub-core/osdep/linux/hostdisk.c
> > +++ b/grub-core/osdep/linux/hostdisk.c
> > @@ -31,6 +31,7 @@
> >   #include <grub/misc.h>
> >   #include <grub/i18n.h>
> >   #include <grub/list.h>
> > +#include <grub/osdep/major.h>
> >   #include <stdio.h>
> >   #include <stdlib.h>
> > @@ -105,6 +106,13 @@ sysfs_partition_path (const char *dev, const char *entry)
> >     char *buf = NULL;
> >     size_t len = 0;
> >     char *path = NULL;
> > +  struct stat st;
> > +  int ret;
> > +
> > +  ret = stat(dev, &st);
> > +  if (ret == 0 && S_ISBLK(st.st_mode))
> > +    return xasprintf ("/sys/dev/block/%u:%u/%s",
> > +		      major (st.st_rdev), minor (st.st_rdev), entry);
> >     argv[0] = "udevadm";
> >     argv[1] = "info";
> 
> Now the non-block device case has one stat call more executed each time.

Practically this should not happen imho, as the device here are returned
by grub_guess_root_devices() to which underlying block devices is used
by a given path or mount point.

Thanks,
Michael

> 
> 
> Kind regards,
> 
> Paul
>