Messages in this thread | | | Subject | RE: how do you call userspace syscalls (e.g. sys_rename) from inside kernel | Date | Mon, 11 Oct 2004 09:13:06 +1000 | From | "Aboo Valappil" <> |
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Hi,
In the past I looked in to open, read and write a file from a kernel module. But problem I faced using the kernel function was that it checks for the permissions of the file and path against the "current" process. For eg: open_namei() function ... My requirement was to open the file regardless of the permissions on the file and also not by modifying task_struct of the current process to change the permissions first ! I also wanted not associate the file with the current/any processes.
Any ideas on this ?
Then I thought of using a work around and avoid opening files in kernel mode.
Thanks
Aboo
-----Original Message----- From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Luke Kenneth Casson Leighton Sent: Saturday, October 09, 2004 1:35 AM To: Fabiano Ramos Cc: linux-kernel@vger.kernel.org Subject: Re: how do you call userspace syscalls (e.g. sys_rename) from inside kernel
On Fri, Oct 08, 2004 at 10:07:04AM -0300, Fabiano Ramos wrote: > On Fri, 2004-10-08 at 14:04 +0100, Luke Kenneth Casson Leighton wrote: > > could someone kindly advise me on the location of some example code in > > the kernel which calls one of the userspace system calls from inside the > > kernel? > > > > alternatively if this has never been considered before, please could > > someone advise me as to how it might be achieved? > > > > you cannot do that. For every sys_xx there is a do_xx, that can > be called from inside the kernel. so, there's a do_rename (yes i found that and ISTRC that when i used it i can't exactly remember what the problem was: either i got an error code -14 or i got "warning symbol do_rename not found" when my module was linked together, even though it says EXPORT_SYMBOL(do_rename) in fs/namei.c, so i was forced to cut/paste sys_rename)
and there's a do_open no there isn't, there's filp_open.
and a do_pread64 no there isn't i had to cut/paste sys_pread64 which was okay because it's pretty basic, just call vfs_read.
and a do_mkdir no there isn't so i had to cut/paste that.
basically what i am doing is writing a file system "proxy" module which re-calls back into the filesystem with a prefix onto the front of the pathname.
> > [p.s. i found asm/unistd.h, i found the macros syscall012345 > > etc., i believe i don't quite understand what these are for, and > > may be on the wrong track.] > > These are are available for you to make syscalls from user mode > without library support (usually that brand new syscall you added). > They are basically wrappers that expand into C code. _syscallx, > where x is the number of arguments the syscall needs. so, it's for use the other way round. okay, thanks for keeping me off a broken line of enquiry.
[oh, and i'll be abandoning this line of enquiry _entirely_ if i find that supermount-ng can do the same job - namely manage to keep userspace programs happy when users rip out media] -- -- Truth, honesty and respect are rare commodities that all spring from the same well: Love. If you love yourself and everyone and everything around you, funnily and coincidentally enough, life gets a lot better. -- <a href="http://lkcl.net"> lkcl.net </a> <br /> <a href="mailto:lkcl@lkcl.net"> lkcl@lkcl.net </a> <br />
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