I want to create a virtual device in Linux with various functions that execute given temporarily defined configuration, and even on inspection of the data itself. I want this to be presentable as a block device to a KVM instance. Where could I get started learning how to do this?
You can start looking at this documentation An introduction to block device drivers
The best book is Linux Device Driver version 3, which is quite old now, but, a new release will happen very soon.
Linux Device Drivers, 4th Edition
You can use losetup to create virtual block devices on Linux:
losetup filename
will create /dev/loop0 which reads and writes from filename. The size of the device is the same as the size of filename.
You can inspect the data by watching the file.
Related
I want to write a linux inspection tool to check the usb device usage records on a certain machine. Parsing the dmesg method can obtain the usb usage record from the system startup to the present, and does not use dmesg -c to clear the dmesg information. So the point of the question is whether there is a place on the Linux system that records all USB usage records in the system, just like the Windows system writes this in the registry.
Linux doesn't natively provide this functionality. It isn't seen as an intrinsically important feature to have, and as mentioned, it can be done easily with a udev rule for those who want it. It's generally assumed that anyone with physical access to the machine can read any unencrypted data on it and execute arbitrary code on it if it's running, so logging USB devices isn't really an effective security measure.
If you want to see the recent history, you can check the kernel log (often /var/log/kern.log) to read the recent and older entries that the kernel has output when a USB device has been inserted. Do note that these are rotated periodically, so they won't provide the entire history of the system.
I have a task to make a virtual device under a real one with the help of device mapper kernel module. Virtual device must transfer any request to a real device, so both devices must be equal.
In prospective I should be able to control requests, so I wrote kernel module, representing device mapper target, using this article.
After making module and inserting it (insmod command) I setup my device (dmsetup create). Then do mount and can work with a real device through just created virtual.
But the question is how to repeat above mentioned instructions in boot time? I'd like to use my virtual device as a general one (by changing fstab, I guess).
Thanks in advance!
If you are going to use your device as the root filesystem, you need to create an initramfs that sets it up. Basically a shell script that issues dmsetup commands, followed by a mount and finally pivot_root to the new filesystem.
There was a discussion on the dm-devel mailing list last year on how to do this in the Linux kernel without an initramfs, by specifying mapper lines on the kernel command line. This is they way Chrome OS does it, because they can't/won't use an initramfs. See here for documentation of this feature. The functionality was never merged though.
The patch series was updated and resubmitted in May 2017. Hopefully we will eventually see it merged in some form or other.
If you are not going to use your device as the root filesystem, you can still use the same approach if you want, but there might be easier ways.
I came across this article
https://scaryreasoner.wordpress.com/2012/01/26/messing-around-with-linux-pci-hotplug/
which is a FAKE hotplug-unplug feature in windows. The author describes that by writing 0/1 to power file the device is plugged/unplugged.
On windows we can disable/enable device using device manager.
Is fakephp hotplug-unplug driver in Linux is same as device disabe/enable feature in Windows?
Fakephp driver, which is already removed from upstream since the PCI core starts to do the same if asked, does logical removal from the system. Keep in mind that power is still goes to the device, though you might change it through PCI configuration space.
My question is pretty much the same as -
How to create a virtual file?
except I want to do it in Linux instead. I imagine what I need to do is create a virtual device and point the application logging to that device. I'd like to write the device in python or ruby or something else interpreted, if possible.
check out named pipes http://en.wikipedia.org/wiki/Named_pipe
Use mknod. You can create a socket file which your apps can write too. And your logging app would connect to the socket to read from it.
Mocking usb devices using umockdev
Umockdev is a linux based application which record the behaviour as well as properties of hardware and run the software independent of actual hardware it is running on. Hardware devices can be simulated in virtual environments
without disturbing the whole system.It currently supports sysfs, uevents, basic support for /dev devices, and recording/mocking usbdevfs ioctls (for PtP/MTP devices).
umockdev home page
source code and examples
I'm looking for either a kernel mode call that I can make from a driver, a userland utility, or a system call that will ask the Kernel to look at the PCI bus and either completely re-run its initialization, or initialize a specific device. Specifically, I need the Kernel to recognize a device that was added to the bus after boot and then configure its address space, interrupt, and other configuration parameters, and finally enable the device so that I can load the driver for it (unless this all happens as part of the driver load).
I'm stuck on the 2.4.x series Kernel for this, and am currently working with 2.4.20, but will be moving to 2.4.37 if it matters. The distro is a stripped down Red Hat 7.3 running in a ram disk, but I can add in whatever tools are needed to get this working (as long as they play nice with 2.4 series).
If some background would help clarify what I'm trying to do: From a cold boot, once in Linux I use GPIO to program an FPGA. Part of the FPGA, once programmed, implements a simple PCI device. Currently, after programming the FPGA, I reboot the system and Linux recognizes the device after coming up and loads the driver for it.
Instead of needing that reboot, I'd like to simply ask the Kernel to do whatever it does during boot up to find PCI devices (I have the Kernel configured to find PCI devices on its own, instead of asking the BIOS for that information, so the BIOS won't need to know about this device (I hope)).
I believe that Linux is capable of seeing the device after it is programmed but before a reboot, because scanpci will show the device after I program it, as will lspci -H 1. I just need a way to get it into /proc/pci, configured and enabled.
This below command will help the user to rescan it complete root hub.
echo "1" > /sys/class/pci_bus/0000\:00/rescan
You could speed up the reboot with kexec, if you don't figure out how to get the PCI scan redone. You could ask this on the LKML, if you haven't already.
unloading/reloading the module doesn't help, does it?
http://www.linuxjournal.com/article/5633 suggests you should be able to do it with 2.4 kernels using pcihpfs.
If that isn't working, maybe the driver doesn't support hotplug?
It would probably crash the system if you reconfigured the addresses of other PCI devices while they are in use.
A better way would be to just configure the new card. If your kernel has support for Cardus devices, it already knows how to configure a newly-inserted PCI device (which is what Cardbus is). You just need to figure out how to get the kernel to do it...
It should be possible for a kernel module to do this. Even if you can't get built-in hotplug code, you should be able to set the pci resources using calls to pci_bus_write_config_dword() and friends. There is probably some IRQ routing setup to do as well.