On Tue, 05 Aug 2003 10:15:24 +0900, kjw7579 wrote: > Let me have time to ask some questions about Linux. > > we can access user buffer within interrupt handler (kernel mode) if we > tocuch segment selectors. > Like these: > mm_segment_t fs; > fs = get_fs(); > set_fs(get_dsc()); > call user space function . > ..... > set_fs(fs); > > My question is: > Can we execute(call) a function of user space within the interrupt handler? No. The code might be swapped out to disk. > reference site http://www.cs.unm.edu/~jotto/linux/linux.html > > Something similar happens with segment selectors when an interrupt takes > place. But in this case there is no assurance that the handler is executing > in the context of the interested process. Suppose though that by some bit > of magic the interrupt handler knows the process's pid and a buffer > address. Then in the case that the handler needs to write data to the > buffer we could do something like the following: [snip] > Here, we do a bit of a context switch by finding out the task structure > associated with the pid (by calling pid2task()and then loading the page > directory pointer for that task into the CR3 register (the latter is the > hardware's entry point to a given process's paging structures). Then we can > use the _fs functions. When we are done we restore the saved context. The > code for updating CR3 was lifted from the SET_PAGE_DIR macro in > include/asm. This is a bad idea. (Don't believe everything you read on the Web.) What if the userspace buffer is swapped out? memcpy_tofs will take a page fault, which is not allowed in interrupt context. See http://kernelnewbies.org/documents/kdoc/kernel-hacking/routines-copy.html http://kernelnewbies.org/documents/kdoc/kernel-hacking/deadlock-recipes.html Wes Felter - wesley@felter.org - http://felter.org/wesley/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
