On Wed, 21 Jun 2006, Zoran Marceta wrote:
> I was looking at catching a signal using usbfs to tell when a device has been
> detached.
> I used an ioctl call with USBDEVFS_DISCSIGNAL to set a signal handler, and I
> was able to detect the detachment.
> >From inode.c (drivers/usb/core/inode.c) file in kernel source I concluded
> >that disc_signal.context is copied
> into si_addr field of siginfo_t structure, but when signal handler was called
> (when I remove USB device)
> I'm always get NULL in info->si_addr (it is not value that I put into
> disc_signal.context field).
...
> After analyzing real-time signal handling in kernel (kernel/signal.c) I
> modified function usbfs_remove_device in
> drivers/usb/core/inode.c file at line 699.
>
> static void usbfs_remove_device(struct usb_device *dev)
> {
> .
> .
> .
> if (ds->discsignr) {
> sinfo.si_signo = ds->discsignr; /* SIGPIPE replaced with
> ds->discsignr */
> sinfo.si_errno = EPIPE;
> sinfo.si_code = SI_ASYNCIO;
> sinfo.si_addr = ds->disccontext;
> kill_proc_info_as_uid(ds->discsignr, &sinfo, ds->disc_pid,
> ds->disc_uid, ds->disc_euid);
> }
> .
> .
> }
>
> Into field si_signo of siginfo_t structure instead of SIGPIPE I put
> ds->discsignr value.
>
> After this change in kernel source I was able to get correct value (equal to
> disc_signal.context) in si_addr field in signal handler.
> Kernel version is 2.6.16-1.2115_FC4. I check latest kernel stable version
> 2.6.17.1 and it has same code in inode.c file.
>
> Is this a bug in usb device removal signal generating or I something missed
> in signal handler registering.
It looks like you are right and this is a bug in inode.c.
It's also not clear why si_errno is set to EPIPE, but I guess that's as
good as anything else. There's a corresponding line in devio.c:
sinfo.si_errno = as->urb->status;
Since urb->status is a negative error code, this should really be
sinfo.si_errno = - as->urb->status;
But such a change would be visible to user programs.
Alan Stern
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