On Tue, Feb 24, 2009 at 3:38 AM, Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx> wrote: > Le Tue, 24 Feb 2009 09:11:53 +0800, > Peter Teoh <htmldeveloper@xxxxxxxxx> a écrit : > >> But then it also puzzled me, because ioctl() in user space required a >> open file descriptor as the first parameter, which is derived from >> open() (as specified from "man ioctl"). so then how is the open() >> from userspace passed down to kernel? > > When userspace uses the open() system call, the kernel function > sys_open() gets called. This kernel function does all the job, and > calls the ->open() operation of the device driver if it exists. > Otherwise, it just doesn't call it, and it works perfectly fine. The > sys_open() function does all what's needed, the ->open() operation is > only here *if* your device driver needs to do something when the device > is opened. This operation is optional. > > sys_open() > http://lxr.free-electrons.com/source/fs/open.c#L1032 > > calls > > do_sys_open() > http://lxr.free-electrons.com/source/fs/open.c#L1010 > > which calls > > do_filp_open() > http://lxr.free-electrons.com/source/fs/namei.c#L1637 > > which calls > > nameidata_to_filp() > http://lxr.free-electrons.com/source/fs/open.c#L918 > > which calls > > __dentry_open() > http://lxr.free-electrons.com/source/fs/open.c#L793 > > which does > > 823 if (!open && f->f_op) > 824 open = f->f_op->open; > 825 if (open) { > 826 error = open(inode, f); > 827 if (error) > 828 goto cleanup_all; > 829 } > > (ouf) > > Sincerly, > > Thomas Thank you Thomas, I think the lxr source code navigator is really useful, as compared with "vi" :-). Thank you for the contribution :-). -- Regards, Peter Teoh -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
