Re: [PATCH] kobject_uevent: add uevent_helper exist check

[zhoumin]

Hi Andrew,

Thank you for your feedback.

> Is there any measurable reduction in boot time?

This depends on the number of uevent and the performance of the device. 
In fact, I found this issue during a project to optomize boot time,
and on my embedded device, it can be optimized by at least 2 seconds.

> Cached in a static variable.  So if a uevent helper later becomes
> available, we won't know that and a reboot will be needed?

The static variable is used to avoid repeatedly checking for uevent_helper 
after the rootfs is mounted and uevent_helper is detected.

As for the uevent before the rootfs is mounted, that is another issue.
Whether I submit this patch or not, system always miss these uevent, because
queue is not used to handle this currently. In fact, I have also noticed
this problem, but based on experience, this seems to cause no issue.

> I wonder if this is the official/preferred way of detecting the
presence of a file.

For only checking file existence, kern_path is a sufficiently simple
approach, you can find it in many kernel lookup functions.

Let me know if you have further suggestions.

Best regards,  
zhoumin