[libcamera-devel,v2,1/2] libcamera: v4l2_device, v4l2_videodevice: call open system call directly

2409 diff mbox series

We are preparing to integrate the V4L2 adaptation layer, which will
intercept open() calls (among others) via LD_PRELOAD. To prevent
libcamera's own open() calls from being intercepted, replace them with a
direct syscall.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

---
No change in v2
---
 src/libcamera/v4l2_device.cpp      | 3 ++-
 src/libcamera/v4l2_videodevice.cpp | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

Hi Paul,

Thank you for the patch.

On Sun, Dec 08, 2019 at 11:56:02PM -0500, Paul Elder wrote:
> We are preparing to integrate the V4L2 adaptation layer, which will
> intercept open() calls (among others) via LD_PRELOAD. To prevent
> libcamera's own open() calls from being intercepted, replace them with a
> direct syscall.
> 
> Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

We may want to later use syscall() for more of our calls in order to
improve performances. I'm in particular thinking about ioctl(). We
should then provide a helper to do so, but for now, I think using
syscall() directly is fine.

> ---
> No change in v2
> ---
>  src/libcamera/v4l2_device.cpp      | 3 ++-
>  src/libcamera/v4l2_videodevice.cpp | 3 ++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> index 0452f801..f16931a3 100644
> --- a/src/libcamera/v4l2_device.cpp
> +++ b/src/libcamera/v4l2_device.cpp
> @@ -11,6 +11,7 @@
>  #include <iomanip>
>  #include <string.h>
>  #include <sys/ioctl.h>
> +#include <sys/syscall.h>
>  #include <unistd.h>
>  
>  #include "log.h"
> @@ -75,7 +76,7 @@ int V4L2Device::open(unsigned int flags)
>  		return -EBUSY;
>  	}
>  
> -	int ret = ::open(deviceNode_.c_str(), flags);
> +	int ret = syscall(SYS_open, deviceNode_.c_str(), flags);

SYS_open is deprecated (but still supported of course) in favour of
SYS_openat. Should we already switch to

	int ret = syscall(SYS_openat, AT_FDCWD, deviceNode_.c_str(), flags);

? glibc does so. I'm also wondering if we should set O_LARGEFILE
unconditionally, but that seems to need some more research.

>  	if (ret < 0) {
>  		ret = -errno;
>  		LOG(V4L2, Error) << "Failed to open V4L2 device: "
> diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> index 99213075..2dff3d3c 100644
> --- a/src/libcamera/v4l2_videodevice.cpp
> +++ b/src/libcamera/v4l2_videodevice.cpp
> @@ -13,6 +13,7 @@
>  #include <string.h>
>  #include <sys/ioctl.h>
>  #include <sys/mman.h>
> +#include <sys/syscall.h>
>  #include <sys/time.h>
>  #include <unistd.h>
>  #include <vector>
> @@ -1427,7 +1428,7 @@ int V4L2M2MDevice::open()
>  	 * as the V4L2VideoDevice::open() retains a handle by duplicating the
>  	 * fd passed in.
>  	 */
> -	fd = ::open(deviceNode_.c_str(), O_RDWR | O_NONBLOCK);
> +	fd = syscall(SYS_open, deviceNode_.c_str(), O_RDWR | O_NONBLOCK);

Same here. With this addressed (or not if you think it's not needed),

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

>  	if (fd < 0) {
>  		ret = -errno;
>  		LOG(V4L2, Error)