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On Sat, 9 Nov 2013 12:29:49 +0000 (UTC) |
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Duncan <1i5t5.duncan@×××.net> wrote: |
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> |
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> udev creates usb devices in /dev/bus/usb. Each usb port is a (three-digit |
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> sequentially numbered) directory, |
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> Libusb, meanwhile, has been updated to work with the /dev/bus/usb/ tree, |
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> so AFAIK that's what you need to create... somehow. |
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> |
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On Sat, 9 Nov 2013 16:11:48 -0600 |
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Barry Schwartz <chemoelectric@×××××××××××××.org> wrote: |
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> |
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> Maybe you can run it once even as a non-daemon just to create the |
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> device, similarly to running rescan-scsi-bus. |
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> |
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Well, it works! That is, I can start udev as a daemon, plug in my |
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scanner, and udev will tell me what the major and minor numbers of the |
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scanner device node. Then I can use my scanner with libusb and SANE. |
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I thought that udev would also create the device node, but for some |
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reason it does not. However, I can create the device manually in the /dev |
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tree and then SANE is able to detect the scanner. |
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Thanks especially to Duncan for his info on the /dev/bus/usb/001 ... |
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location. I can manually create, for example, /dev/bus/usb/001 |
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using the major/minor numbers reported by udev. Then I am in |
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business for scanning. |
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Actually, I can just create a whole series of nodes under /dev/bus/usb |
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with the same major number and an incremental minor number. This |
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will eliminate the need to use udev entirely. Whenever I plug in my |
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scanner one of those nodes will be relevant. |
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But the whole process illustrates that udev is not really necessary. |
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The scanner is accessed through a device node in the /dev tree |
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and there is no reason why udev must create this node. As long |
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as the major/minor numbers are known (and the char or block characteristic) |
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then anything can create the node. IOW, the kernel access is the |
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same as always. Only these user space programs impose these node |
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constraints. |
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I wonder if I can determine the major/minor numbers in some other way. |
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Maybe the /sys tree has that information. If so, then I could |
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completely script the process without using udev. |
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Thanks to all for the contribution. |
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Frank Peters |
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