Re: [Libmtp-discuss] udev and libmtp: detect a new mtp device based on its USB interface descriptor

[<la...@no...>]

Hi Linus,
Thanks. Since adding '02' is ok and do not incur performance decrease, that's fine for us. Thanks.

Regards,
Lan Liu

-----Original Message-----
From: ext Linus Walleij [mailto:lin...@gm...] 
Sent: Tuesday, January 25, 2011 2:57 AM
To: lib...@li...
Cc: Li Feng.5 (Nokia-MS/Beijing); Tarvainen Miska (Nokia-MS/Beijing); Quadros Roger (Nokia-MS/Helsinki); Wang Hongyu (Nokia-MS/Beijing)
Subject: Re: [Libmtp-discuss] udev and libmtp: detect a new mtp device based on its USB interface descriptor

2011/1/24  <la...@no...>:

> Adding '02' to the 'ATTR{bDeviceClass}' of above rule would be a direct solution to this.

I've added this in the latest git...

> But if we are worried that querying an interface descriptor of a device, would affect
> the device bootup time, esp, when this device has multi interfaces, we can firstly
> resort to the information under sysfs, without operating with this device, to check
> if it is a mtp device. If this check failed, then invoke 'mtp-probe' to do further check.

The time problem is not with the probing of the interfaces, this is fast.

The problem is invoking the program, mtp-probe, which is ~9 KB
(two pages) of code needing to be paged in from the file system/cache.

IIRC the previous approach for checking the interface invoked a shell,
which is (bash) 877 KB.

The shell is usually paged into memory though, so I dunno. If you can
benchmark it, it'd be great.

Linus

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