strace and ALSA ioctls

strace and ALSA ioctls

[Lee Revell]

I have never seen strace correctly identify a single ALSA ioctl.  This
makes debugging a serious PITA.  Is it fixable?

ioctl(3, USBDEVFS_CONTROL, 0xbfe13958)  = 0
ioctl(3, UI_DEV_CREATE, 0xbfe13a70)     = 0
close(3)                                = 0
stat64("/usr/share/alsa/alsa.conf", {st_mode=S_IFREG|0644,
st_size=7501, ...}) = 0
open("/dev/snd/controlC0", O_RDONLY)    = 3
close(3)                                = 0
open("/dev/snd/controlC0", O_RDWR)      = 3
ioctl(3, USBDEVFS_CONTROL, 0xbfe138f8)  = 0
fcntl64(3, F_GETFL)                     = 0x2 (flags O_RDWR)
fcntl64(3, F_SETFL, O_RDWR|O_NONBLOCK)  = 0
ioctl(3, USBDEVFS_RELEASEINTERFACE, 0xbfe139e4) = 0
ioctl(3, USBDEVFS_RELEASEINTERFACE, 0xbfe139e4) = 0
ioctl(3, USBDEVFS_CONNECTINFO, 0xbfe136d0) = 0
ioctl(3, USBDEVFS_IOCTL, 0xbfe13230)    = 0
ioctl(3, USBDEVFS_CONNECTINFO, 0xbfe136d0) = 0
ioctl(3, USBDEVFS_IOCTL, 0xbfe13230)    = 0
ioctl(3, USBDEVFS_IOCTL, 0xbfe13230)    = 0
ioctl(3, USBDEVFS_CONNECTINFO, 0xbfe136d0) = 0
ioctl(3, USBDEVFS_IOCTL, 0xbfe13250)    = 0
ioctl(3, USBDEVFS_CONNECTINFO, 0xbfe136d0) = 0
ioctl(3, USBDEVFS_IOCTL, 0xbfe13230)    = 0
ioctl(3, USBDEVFS_IOCTL, 0xbfe13230)    = 0
ioctl(3, USBDEVFS_CONNECTINFO, 0xbfe136d0) = 0
ioctl(3, USBDEVFS_IOCTL, 0xbfe13250)    = 0

etc

Lee



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Re: strace and ALSA ioctls

[Takashi Iwai]

At Thu, 18 May 2006 11:41:48 -0400,
Lee Revell wrote:
> 
> I have never seen strace correctly identify a single ALSA ioctl.  This
> makes debugging a serious PITA.  Is it fixable?

Quite unlikely.  Some ioctl commands are indeed identical with these
USBDEVFS_*.  This happened since we didn't care about the collision
and found it too late.

In the kernel side this is no problem because the ioctl cmd is bound
to each driver's ioctl op.  But, from user-space, there is no way to
distinguish properly.


Takashi

> 
> ioctl(3, USBDEVFS_CONTROL, 0xbfe13958)  = 0
> ioctl(3, UI_DEV_CREATE, 0xbfe13a70)     = 0
> close(3)                                = 0
> stat64("/usr/share/alsa/alsa.conf", {st_mode=S_IFREG|0644,
> st_size=7501, ...}) = 0
> open("/dev/snd/controlC0", O_RDONLY)    = 3
> close(3)                                = 0
> open("/dev/snd/controlC0", O_RDWR)      = 3
> ioctl(3, USBDEVFS_CONTROL, 0xbfe138f8)  = 0
> fcntl64(3, F_GETFL)                     = 0x2 (flags O_RDWR)
> fcntl64(3, F_SETFL, O_RDWR|O_NONBLOCK)  = 0
> ioctl(3, USBDEVFS_RELEASEINTERFACE, 0xbfe139e4) = 0
> ioctl(3, USBDEVFS_RELEASEINTERFACE, 0xbfe139e4) = 0
> ioctl(3, USBDEVFS_CONNECTINFO, 0xbfe136d0) = 0
> ioctl(3, USBDEVFS_IOCTL, 0xbfe13230)    = 0
> ioctl(3, USBDEVFS_CONNECTINFO, 0xbfe136d0) = 0
> ioctl(3, USBDEVFS_IOCTL, 0xbfe13230)    = 0
> ioctl(3, USBDEVFS_IOCTL, 0xbfe13230)    = 0
> ioctl(3, USBDEVFS_CONNECTINFO, 0xbfe136d0) = 0
> ioctl(3, USBDEVFS_IOCTL, 0xbfe13250)    = 0
> ioctl(3, USBDEVFS_CONNECTINFO, 0xbfe136d0) = 0
> ioctl(3, USBDEVFS_IOCTL, 0xbfe13230)    = 0
> ioctl(3, USBDEVFS_IOCTL, 0xbfe13230)    = 0
> ioctl(3, USBDEVFS_CONNECTINFO, 0xbfe136d0) = 0
> ioctl(3, USBDEVFS_IOCTL, 0xbfe13250)    = 0
> 
> etc
> 
> Lee
> 
> 
> 
> -------------------------------------------------------
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> 


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Re: strace and ALSA ioctls

[Lee Revell]

On Thu, 2006-05-18 at 17:47 +0200, Takashi Iwai wrote:
> At Thu, 18 May 2006 11:41:48 -0400,
> Lee Revell wrote:
> > 
> > I have never seen strace correctly identify a single ALSA ioctl.  This
> > makes debugging a serious PITA.  Is it fixable?
> 
> Quite unlikely.  Some ioctl commands are indeed identical with these
> USBDEVFS_*.  This happened since we didn't care about the collision
> and found it too late.
> 
> In the kernel side this is no problem because the ioctl cmd is bound
> to each driver's ioctl op.  But, from user-space, there is no way to
> distinguish properly.
> 

But for some ioctls it says:

ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon
echo ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon
echo ...}) = 0

So it seems that strace is aware of some of the collisions but not
others?

Lee



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Re: strace and ALSA ioctls

[Takashi Iwai]

At Thu, 18 May 2006 12:12:06 -0400,
Lee Revell wrote:
> 
> On Thu, 2006-05-18 at 17:47 +0200, Takashi Iwai wrote:
> > At Thu, 18 May 2006 11:41:48 -0400,
> > Lee Revell wrote:
> > > 
> > > I have never seen strace correctly identify a single ALSA ioctl.  This
> > > makes debugging a serious PITA.  Is it fixable?
> > 
> > Quite unlikely.  Some ioctl commands are indeed identical with these
> > USBDEVFS_*.  This happened since we didn't care about the collision
> > and found it too late.
> > 
> > In the kernel side this is no problem because the ioctl cmd is bound
> > to each driver's ioctl op.  But, from user-space, there is no way to
> > distinguish properly.
> > 
> 
> But for some ioctls it says:
> 
> ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon
> echo ...}) = 0
> ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon
> echo ...}) = 0
> 
> So it seems that strace is aware of some of the collisions but not
> others?

Maybe depends on the strace version.  strace has a string table for
each ioctl entry.

Hm, looking at the source, the script included there doesn't handle
ioctls defined via enum correctly.  Too bad.


Takashi


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