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Check V4L2_CAP_VIDEO_CAPTURE when enumerating capture devices on Linux

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The side effect of not filtering on V4L2_CAP_VIDEO_CAPTURE is that
every device is enumerated twice. Because we look up devices by name,
and the device that supports V4L2_CAP_VIDEO_CAPTURE seems to always
appear first in /dev/video, this does not seem to end up with us ever
choosing an inappropriate device. We might get away with just filtering
device names from the list, but if the order of devices ever changed in
/dev/video there could be problems.

Bug: webrtc:11641
Change-Id: I16fee4edc873838ed4643ee16a8bbc699d6bbcf5
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/176460
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Commit-Queue: Dan Minor <dminor@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31508}
This commit is contained in:
Dan Minor 2020-06-03 13:13:30 -04:00 committed by Commit Bot
parent d592575698
commit b64ecd9960
1 changed files with 20 additions and 1 deletions
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21
modules/video_capture/linux/device_info_linux.cc
View File

@ -47,11 +47,19 @@ uint32_t DeviceInfoLinux::NumberOfDevices() {
uint32_t count = 0;
char device[20];
int fd = -1;
struct v4l2_capability cap;
/* detect /dev/video [0-63]VideoCaptureModule entries */
for (int n = 0; n < 64; n++) {
sprintf(device, "/dev/video%d", n);
if ((fd = open(device, O_RDONLY)) != -1) {
// query device capabilities and make sure this is a video capture device
if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0 ||
!(cap.device_caps & V4L2_CAP_VIDEO_CAPTURE)) {
close(fd);
continue;
}
close(fd);
count++;
}
@ -74,9 +82,16 @@ int32_t DeviceInfoLinux::GetDeviceName(uint32_t deviceNumber,
char device[20];
int fd = -1;
bool found = false;
struct v4l2_capability cap;
for (int n = 0; n < 64; n++) {
sprintf(device, "/dev/video%d", n);
if ((fd = open(device, O_RDONLY)) != -1) {
// query device capabilities and make sure this is a video capture device
if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0 ||
!(cap.device_caps & V4L2_CAP_VIDEO_CAPTURE)) {
close(fd);
continue;
}
if (count == deviceNumber) {
// Found the device
found = true;
@ -92,7 +107,6 @@ int32_t DeviceInfoLinux::GetDeviceName(uint32_t deviceNumber,
return -1;
// query device capabilities
struct v4l2_capability cap;
if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0) {
RTC_LOG(LS_INFO) << "error in querying the device capability for device "
<< device << ". errno = " << errno;
@ -153,6 +167,11 @@ int32_t DeviceInfoLinux::CreateCapabilityMap(const char* deviceUniqueIdUTF8) {
// query device capabilities
struct v4l2_capability cap;
if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == 0) {
// skip devices without video capture capability
if (!(cap.device_caps & V4L2_CAP_VIDEO_CAPTURE)) {
continue;
}
if (cap.bus_info[0] != 0) {
if (strncmp((const char*)cap.bus_info, (const char*)deviceUniqueIdUTF8,
strlen((const char*)deviceUniqueIdUTF8)) ==