[systemd-devel] udev blkid check on mmcblk0boot0 and boot1

[Jeremy Linton]

Hi,

On 2/2/21 1:46 PM, Alan Perry wrote:
> 
> On 2/2/21 1:55 AM, Lennart Poettering wrote:
>> On Mo, 01.02.21 16:36, Alan Perry (alanp at snowmoose.com) wrote:
>>> Hi, Per the udev rules, the blkid builtin is run on mmcblk*boot* 
>>> devices to look for partition and filesystem. Those devices contain 
>>> hardware-specific boot information and are unlikely to have anything 
>>> on them that blkid would identify. Why isn't there a rule to exclude 
>>> them from blkid? Is there some case that I am missing? 
>> Probably noone who cares about MMC enough prepped a patch for this so 
>> far. Also it probably doesn't matter too much... I mean, if blkid 
>> doesn't find anything it doesn't find anything, so not much bad 
>> happened? If this matters to you, and it's really clear that there is 
>> unlikely anything blkid-recognizable on it, then by all means, please 
>> send a PR! 
> 
> I have been looking into a problem that we occasionally see with hangs 
> at boot time during the probe of
> mmcblk0boot0. Doing some searching, I have seen reports of similar hangs 
> over the years, so I see a
> potential benefit of not doing the probe.
> 
> Is the blkid/libblkid code robust enough that it could sanely handle 
> whatever hardware-specific collection of
> bits representing the boot configuration that happens to be there?

Well I guess someone could put something like an efi system partition on 
a mmc boot. In which case you would want to probe it.

OTOH, this really sounds like a determination of why the system is 
hanging when its touching those partitions is in order.

(hang as in, does the kernel have a bug, or is it trying to update a 
fat/etc dirty bit on a read only partition, etc?)


> 
> I had been planning on sending a PR. As I said, the idea seemed so 
> obvious to me that I wanted to confirm that
> it hadn't been considered and rejected at some point in the past before 
> I did.
> 
> As far as the change itself, would it be something as simple as adding:
> 
> KERNEL!="mmcblk[0-9]boot[0-9]"
> 
> before the last clause of this rule:
> 
> # probe filesystem metadata of disks
> KERNEL!="sr*", IMPORT{builtin}="blkid"
> 
> 
> alan
> 
> 
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