I am embarking on a programming project that will need to confirm device identity of removable media (e.g. usb thumb drives) before it will go on to do a bunch of other cool stuff.
Some friends of mine pointed me towards using the Serial Number, and preliminary testing using the udevadm command indicates that this should work. I did some additional checking and it appears that if I can get the software working with libudev then it should (minimally) compile on ubuntu, slackware and gentoo, which would be a really nice benefit.
So I used bing to find a tutorial and got the Signal 11 site (http://www.signal11.us/oss/udev/) it's a very well-written tutorial. It actually seems to have everything I need. I download the code. Fix a couple of platform-specific bugs and then compile. BOOM! Gcc compiles without errors. So far so good.
But when I try to run it, it kicks up a couple of bugs, and I realize that I need to read some more tutorials so that I can understand libudev well enough to fix the bugs, and to turn out working software. Problem is that there really ISN'T any other tutorials (that I can find) and the kernel.org site that is the (only known?) site of the library documentation is down after a recent server compromise.
I considered just issuing udevadm directives to system() and then parsing results, but that's a really hackish way to put software together, and I am planning on releasing this to the community when I'm finished writing.
So how best for me to learn libudev??
libudev is quite simple library. After reading library you've mentioned and using API documentation (site should be soon up) I was able to get what I wanted. udevadm is great help, after issuing # udevadm info --query=all --name=/path/to/dev you'll get all information that udev has about this device and what's more important, these are parameters used in property functions (e.g. udev_device_get_property_value(device, "ID_VENDOR")). So best way to learn libudev is to start using it with help of signal11 tutorial, API documentation and udevadm informations.
EDIT: libudev is currently part of systemd - documentation is available as manual pages - https://www.freedesktop.org/software/systemd/man/libudev.html#
For those looking in 2023...
As Maciej pointed out, libudev is now a part of systemd.
According to:
https://www.freedesktop.org/software/systemd/man/libudev.html#
...this library is supported, but should not be used in new projects.
Please see sd-device(3) for an equivalent replacement with a more
modern API.
Documentation for sd-device:
https://www.freedesktop.org/software/systemd/man/sd-device.html#
Related
I'm working on a project, implementing everything in C language. As a part of the project, we need to be able to control and configure firewalld, firewall of the current system.
firewalld is implemented in Python and an interface is available. However, we don't want to make Python calls from C or vice versa.
There are command line tools to configure firewalld (e.g. firewall-cmd) but we don't want to make such calls from C either.
I recently started working on firewalld, I don't know much about its internals. I've read that it uses D-Bus, I also don't know much about D-Bus.
There is a C library developed by Thomas Woerner: libfirewall.
However, it's been more than a year and a half since the last commit so it's not maintained. Other than libfirewall, I don't know any firewalld interface in C.
I gave libfirewall a shot. It got me some problems when both compiling and running the examples and I still have problems to resolve. Is it worth to continue with libfirewall? Should I use it?
Is there any other interface that I'm not aware of?
Possibly naive question due to lack of understanding of D-Bus: I thought, maybe, with a D-Bus interface, I can issue commands to firewalld. Can it be done? (i.e. Does D-Bus work like that?) Can we write a program that mimics, say firewall-cmd, and interacts with D-Bus in the same way and at the end allows us to control firewalld?
If this is possible, how to do it and what to use? libdbus and GDBus have relatively good documentation although libdbus requires good deal of effort. They even said "If you use this low-level API directly, you're signing up for some pain." in the documentation. In any case I'll be in need of examples or any kind of text demonstrating their usage.
How should I approach this problem?
Yes, you can issue commands to firewalld via D-Bus. I haven't checked but expect that firewall-cmd is itself implemented as a D-Bus client.
The D-Bus API is extensively documented: https://firewalld.org/documentation/man-pages/firewalld.dbus.html. The documentation should give you a rough idea what can be accomplished through the API. You could try the D-Bus debugger d-feet to interact with firewalld without any code.
GDBus is definitely the easiest way use D-Bus from C but it's still not trivial and firewalld is a fairly complex API: Using it may require some expertise (completely depending on what you need to do).
I am modifying the code for glibc 2.5. Now since glibc is large and complex, I need to have a really good tool, to see interaction of different parts of the code. I am using Understand for this purpose, but Understood is only valid for 15 days. Afterwards you have to buy it.
So my question is, on web, are there sites where you can interactively understand common code bases such as glibc, gcc, linux kernel etc. I mean where you could search for some function, and then click on a function call to see its definition and such other useful features. I have used Koders.com, but it will only display the code, and is not interactive.
OpenGrok is good. You have to host it yourself though, it's not on the web.
I am interested in delving into Erlang's C source code and try to understand what is going on under the hood. Where can I find info on the design and structure of the code?
First of all, you might want to have a look to Joe Armstrong's thesis, introducing Erlang at a high level. It will be useful to get an idea of what was the idea behind the language. Then, you could focus on the Erlang Run Time System (erts). The erlang.erl module could be a good start. Then, I would focus on the applications who constitutes the so-called minimal release, kernel and stdlib. Within the stdlib, have a look on how behaviours are implemented. May I suggest the gen_server.erl module as a start?
A Guide To The Erlang Source
http://www.trapexit.org/A_Guide_To_The_Erlang_Source
The short answer is that there is no good guide. And the code is not very well documented.
I recommend finding someone in your neighbourhood that knows the code reasonably well, and buy them dinner in exchange for a little chat.
If you don't have the possibility to do that, then I recommend starting with the loader.
./erts/emulator/beam/beam_load.c
Some useful information can also be found by pretty printing the beam representation. I don't know whether there is any way to do so supplied by OTP, but the HiPE project has some cheats.
hipe:c(MODULE, [pp_beam]).
Should get you started.
(And I also recommend Joe's book.)
Pretty printer of beam can be done by 'erlc -S', which is equivalent with hipe:c(M, [pp_beam]) mentioned by Daniel.
I also use erts_debug:df(Module). to disassemble the loaded beam code, which are instructions actually been interpreted by the VM.
Sometimes I use a debugger. OTP delivers tools supporting gdb very well. See example usage at http://www.erlang.org/pipermail/erlang-questions/2008-September/037793.html
A little late to the party here. If you just download the source from GitHub the internal documentation is really good. You have to generate some of it using make.
Get the documentation built and most of the relevant source is under /erts (Erlang Run Time System)
Edit: BEAM Wisdoms is also a really good guide but it may or may not be what you're after.
This is my first embedded project, so bear with my ignorance. I've been asked to implement Remote NDIS over USB, using the ColdFire USB-Lite stack by CMX. I've been searching for a long time now, and can't find any clear documentation for this stack.
It comes with some woefully documented sample code and the only useful resource I've been able to find online is this Application Note (PDF) by Eric Gregori.
What I really want is an explanation of all the functions in the API. I can work out how to use them. Does this exist? Can someone point me to it?
EDIT: Nevermind.
After tracing the execution across 14 half-documented source files (from the example program) and scrutinizing a bunch of undocumented variables and buffers, and doing a diff between corresponding files in different projects, I think I finally get it. So I guess stackoverflow.com taught me patience... or something.
The link you referred to doesn't work for me, but the name of the file made me look at the Freescale pages, and if that's not the document you intended to link to, it might be the documentation you need.
Almost the same question as this one here:
What's the easiest way to grab a web page in C?
however the conditions have changed and I need to connect via https, this is a bit more tricky, anyone got any snippets?
I am on a qnx platform, building and compiling additional libraries and rolling it out onto our product is very, very hard given the contraints. So things like libcurl are not possible.
Results:
It turns out I had to install libcurl on QNX after all. This involved installing perl and openSSL to build libcurl, but once that was built it was good to go. This was the least desirable option but it ended up being worth it.
libcurl should be able to handle anything you need to do.
If you're not able to use a library, then I guess you're either forced to cheat, as in "call out to a shell or some other environment that already has this capability". I'm not very familiar with QNX or the environments where it's typically run, not enough to dicount this possibility on my own anyway.
By the way, before skipping this: libcurl is known to build on QNX, so try that before even reading further.
Failing that, taking the question literally, I guess you need to implement the relevant parts of the HTTP protocol yourself. Since you now need secure access too, you're in a world of hurt. You just don't want to implement that type of code on your own, it is a lot of work, many many wheels to re-invent.
At the very least, I'd recommend taking a hard look around to see if any of the things you need to do this are already implemented. This page implies that OpenSSH is available for the QNX platform, which is encouraging.
I was away when you posted this followup question.
I've now posted an SSL-capable example program at http://pastebin.com/f1cd08b33
This needs to be linked against OpenSSL (-lssl) but doesn't need libcurl at all.