[uml-devel] system call accessing the host os
Hi, I'm currently working on a project in which we are using UML to access the host os and perform some operations. More precisely, we would like to have a system call in UML that parses a file in the host os. Since the UML kernel is a host process, I naively thought that I could use regular C directly. Indeed, I was able to create my system call, and then have some other C files compiled using host os headers such as and by putting them in the USER_OBJS list of the Makefile. Unfortunately, I'm having some weird issues that I can't really understand. I can read the file using fread, but only in a buffer that I allocated using um_kmalloc. If I use a buffer allocated by malloc, the fread fails. Then, even if I replace all my mallocs by um_kmallocs, some libc functions (such as sscanf) don't seem to work properly. I guess I'm missing something, but I can't figure out what. If anyone of you can help me, I'd really appreciate, With best regards, Olivier P.S.: I'm using 2.6.15.6 with the latest 2.6.15 patch and the guest kernel runs in skas3 mode. --- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 ___ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
Re: [uml-devel] system call accessing the host os
Well, yes, I could use this. But what I'm actually trying to understand is how to properly execute regular C within the UML kernel to access the host OS. Thks, Olivier On 5 avr. 06, at 19:18, D. Bahi wrote: what about this? http://user-mode-linux.sourceforge.net/iomem.html Olivier Crameri wrote: Hi, I'm currently working on a project in which we are using UML to access the host os and perform some operations. More precisely, we would like to have a system call in UML that parses a file in the host os. Since the UML kernel is a host process, I naively thought that I could use regular C directly. Indeed, I was able to create my system call, and then have some other C files compiled using host os headers such as and by putting them in the USER_OBJS list of the Makefile. Unfortunately, I'm having some weird issues that I can't really understand. I can read the file using fread, but only in a buffer that I allocated using um_kmalloc. If I use a buffer allocated by malloc, the fread fails. Then, even if I replace all my mallocs by um_kmallocs, some libc functions (such as sscanf) don't seem to work properly. I guess I'm missing something, but I can't figure out what. If anyone of you can help me, I'd really appreciate, With best regards, Olivier P.S.: I'm using 2.6.15.6 with the latest 2.6.15 patch and the guest kernel runs in skas3 mode. --- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel? cmd=lnk&kid=110944&bid=241720&dat=121642 ___ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel --- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 ___ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
Re: [uml-devel] system call accessing the host os
Thanks for the answer. I bumped CONFIG_KERNEL_STACK_ORDER to 3, but it doesn't help. I have a system call that does nothing but execute my code to parse my file in the host. When I said that using malloc didn't work, I meant the following: I'm using malloc to allocate a buffer in the UML kernel. I'm not passing a user level buffer to the system call. Then, when I use fread to read my file into this buffer, if I read a small number of bytes, it works. However when I try to fread the entire file (38k), fread returns 0. The same thing using a buffer returned by um_kmalloc works perfectly (i.e. returns 1 and the buffer is filled with the file data). Later on, I use sscanf to parse my buffer. No matter what happens, sscanf returns 0, which is wrong even if there is no error. The exact same code compiled in the host works perfectly. Again, thank you for your help, I really appreciate. Olivier On 4/5/06, Jeff Dike <[EMAIL PROTECTED]> wrote: > On Wed, Apr 05, 2006 at 07:16:22PM +0200, Olivier Crameri wrote: > > Unfortunately, I'm having some weird issues that I can't really > > understand. I can read the file using fread, but only in a buffer > > that I allocated using um_kmalloc. If I use a buffer allocated by > > malloc, the fread fails. Then, even if I replace all my mallocs by > > um_kmallocs, some libc functions (such as sscanf) don't seem to work > > properly. I guess I'm missing something, but I can't figure out what. > > Define "fails" and "don't seem to work properly". > > If your buffers are larger than 128K, then libc malloc gets turned into > UML kernel vmalloc. In this case, the buffer isn't mapped, and > passing it into a system call will make it return -EFAULT. The > easiest workaround for this is to memset the thing immediately after > allocating it. > > Also, if you're using the libc things you're talking about, watch out > for your stack consumption. By default, you get two pages (8K). > printf will completely use it up, so it is unusable in kernel code. > > UML kernel stack size is configurable - CONFIG_KERNEL_STACK_ORDER - > bumping that to 3 will double the kernel stack size. If problems then > go away, then you know that libc is overflowing your stack. > > Jeff > --- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid0944&bid$1720&dat1642 ___ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
Re: [uml-devel] system call accessing the host os
Then, when I use fread to read my file into this buffer, if I read a small number of bytes, it works. However when I try to fread the entire file (38k), fread returns 0. What's the break point between working and non-working? It looks like it's on a page boundary. 4095 bytes is ok, 4096 is not I'm using 2.6.15.6 with the latest 2.6.15 patch from Blaisorblade's website. Regards, Olivier --- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 ___ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
Re: [uml-devel] system call accessing the host os
Great, thanks a lot. Now I understand what's happening. It was actually calling um_vmalloc Olivier On 7 avr. 06, at 01:42, Jeff Dike wrote: On Fri, Apr 07, 2006 at 02:20:00AM +0200, Blaisorblade wrote: No, I made it "greater than 4k" in 2.4.24 time... in fact it's what's happening to him (see his last mail): Oh yeah. In that case, the memset thing I mentioned earlier might help. Jeff --- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 ___ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
