Re: [dm-devel] [patch] mpath_prio_pp

[Kiyoshi Ueda <k-ueda ct jp nec com>]

Hi Veena,

On Wed, 9 Jan 2008 15:15:38 +0530, "T S, Veena (STSD)" wrote:
> Purpose of the patch-
> -- To introduce the prio_callout attribute into the multipath section of
> the configuration file.

The prio_callout feature has been changed to the libprio.
Please check the latest Christophe's git.


> -- To implement the preferred path feature in device mapper.
> 
> Uses of the patch-
> -- Prio_callout attribute in the multipath section allows users to write
> callout routines,which can be specific to a LUN.
> -- When it is known the performance of one of the path is better than
> the other available paths for a particular LUN, the user can set it as
> preferred path.

How about opposite case such as the performance of some paths are
better than the one backup path for a particular LUN?
So if we can specify some preferred paths, that may be more useful.


> +int main(int argc, char * argv[]) 
> +{ 
> + 
> +       char path[FILE_NAME_SIZE]; 
> +       
> +       if(argv[1] && argv[2]) 
> +       { 
> +               if(!strncmp(argv[2],"/dev/",5)) 
> +                       strcpy(path,argv[2]+5); 
> + 
> +               if(!strcmp(path,argv[1]) || !strcmp(argv[1],argv[2])) 
> +               { 
> +                       printf("%u\n", HIGH); 
> +                       return 0; 
> +               } 
> +               else 
> +               { 
> +                       printf("%u\n", LOW); 
> +                       return 0; 
> +               } 
> +       } 
> +       return -1; 
> +} 

This prioritizer looks that we need to specify the preferred path
by devnode or major/minor, right?
If so, it doesn't work reliably.
Both devnode and major/minor may vary for each system reboot.
It's horrible to check and change the config file after every reboot.
We should be able to use more persistent name to specify a path,
though I don't have a good idea now...

Thanks,
Kiyoshi Ueda