Re: /proc/sys/kernel/real-root-dev

[Andrew Clausen]

On Thu, Dec 12, 2002 at 03:47:00AM +0100, Juan Pedro Vallejo wrote:
> Hello.
> 
> # parted /dev/hdc
> Warning: Unable to determine if partitions are mounted via
> /proc/mounts or /etc/mtab.  Make sure you don't attempt to resize or
> modify mounted file systems.  (Even read-only mounted)
> Ignore/Cancel?
> 
> Version 1.6.4. I don't have a /proc/sys/kernel/real-root-dev file, so
> _partition_is_root_device() always fails. Shouldn't it return "I don't
> know" instead, like _mount_table_search() does?.

This isn't quite true.  If there's no /dev/root in /proc/mount, it won't
fail unconditionally.

> And why the checks in _partition_is_mounted_by_path() are not taken
> sequentially?. Like this:

Unfortunately, your code won't work.  (See below)
It does seem easier to follow though.

> static int
> _partition_is_mounted_by_path (const char* path)
> {
>       static int can_probe = 1;
> 
>       if (!can_probe)
>               return 0;
> 
>       /* try first way */
>       switch (_partition_is_root_device (path)) {
>               case 1: return 1;       /* it is here */
>               case 0: return 0;       /* it is not */

Just because you know it isn't the root device doesn't mean you know
it isn't mounted, right?

>       }
>       /* we don't know, try second way */
>       switch (_mount_table_search ("/proc/mounts", path)) {
>               case 1: return 1;       /* it is here */
>               case 0: return 0;       /* it is not */
>       }
>       /* we don't know, try third way */
>       switch (_mount_table_search ("/etc/mtab", path)) {
>               case 1: return 1;       /* it is here */
>               case 0: return 0;       /* it is not */
>       }
>       /* we don't know, try last way */
>       switch (_mount_table_search ("/proc/swaps", path)) {
>               case 1: return 1;       /* it is here */
>               case 0: return 0;       /* it is not */
>       }
> 
>       /* we still don't know, and never will */
>       can_probe = 0;
> 
>       /* ask the animal */
>       return ped_exception_throw (...) != PED_EXCEPTION_IGNORE;
> }
> 
> Also, the message does not mention the other two files it looks at.

It doesn't look at the real-root-dev unconditionally.  (It's
only needed if there's a /dev/root entry in /proc/mounts)  It does
for /proc/swaps though, so I should add that.

Thanks,
Andrew