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

[Jeff Mahoney <jeffm@suse.com>]

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On 7/13/21 1:48 PM, Daniel Kiper wrote:
> On Thu, Jul 08, 2021 at 05:55:58PM +0200, Petr Vorel wrote:
>> 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.
>>
>> 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);
> 
> Missing space between "stat" and "(".
> 
>> +  if (ret == 0 && S_ISBLK(st.st_mode))
> 
> Same for S_ISBLK...
> 
>> +    return xasprintf ("/sys/dev/block/%u:%u/%s",
>> +		      major (st.st_rdev), minor (st.st_rdev), entry);
>>
>>    argv[0] = "udevadm";
>>    argv[1] = "info";
> 
> Do we really need udevadm fallback mechanism? If something went wrong
> here for us I do not expect it will work for udevadm either.

I suspect not.  'udevadm info --query path --name <dev>' does
essentially the same thing but with many more steps and the cost
starting an external program for every block device.  I left it in with
the assumption that it was probably there for a reason and perhaps
udevadm on early udev systems did something more special than just doing
stat + sysfs path building.  I didn't spend any time on validating that
assumption.

-Jeff

-- 
Jeff Mahoney
Director, SUSE Labs Data & Performance


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