On Friday 15 July 2005 11:59, Alex LIU wrote: > Hi,all: > I just modified the kernel thread function in UML 2.6.7 tt mode. I want the > kernel thread go to the user space after finished the kernel function > rather than exit. It's just like a system call return or a return from > fork... Hmm, but where's the caller to return? In most cases it won't exist.
I don't understand what's your purpose, and the behaviour you'd want to reproduce. Sorry, but *which* userspace should it go to? What you're modifying is the execution path of kernel_thread. Now, let's take a call to kernel_thread from the initial thread, before init is executed, or a similar situation (ksoftirqd and such things must surely be kernel_thread'ed from somewhere). Where should it continue? Neither in kernel code because it's now hidden (or it should be, anyhow this isn't supposed to work), nor in userspace code because no one has been specified. Now, surely, there are cases where a userspace context will exist. For instance, modprobe <some module spawning a kernel thread in initialization>, or mount ext3/reiserfs fs. In both cases, the kernel code will spawn a kernel thread; but the userspace caller will already have continued with the system call return code when the kernel thread exits (or, probably, the caller will have died). > But now the problem is that there will be segmentation fault just before > the kernel thread go to the user space. After tracing I found when the > segmentation fault occur, in handle_page_fault function, (!(vma->vm_flags & > VM_GROWSDOWN)) is true and the err is -14. What's the meaning of such > value? Look up in errno headers (/usr/include/asm/errno.h and dependencies). It's EFAULT, which makes sense. No userspace program, so no mapping to use and no registers to execute. -- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade ------------------------------------------------------- SF.Net email is sponsored by: Discover Easy Linux Migration Strategies from IBM. Find simple to follow Roadmaps, straightforward articles, informative Webcasts and more! Get everything you need to get up to speed, fast. http://ads.osdn.com/?ad_id=7477&alloc_id=16492&op=click _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
