From 221b5221185b1ef57ae94c70627a9475e239f77b Mon Sep 17 00:00:00 2001
From: "wu@webrtc.org" <wu@webrtc.org@4adac7df-926f-26a2-2b94-8c16560cd09d>
Date: Wed, 21 Sep 2011 16:57:15 +0000
Subject: [PATCH] Return the number of /dev/video* without trying to open it.

Consider the case when there're /dev/video0 and /dev/video1. But for somereason the video0 is not in a correct state and can't be open. As a result, current NumberOfDevices will return 1, which is fine. However, we will then never be able to get the device we really want - /dev/video1. Consider the code below, the GetCaptureDevice will fail because it calls into DeviceInfoLinux::GetDeviceName(0, ...) which will again try to open the /dev/video0. So the root cause is the mismatching of the NumberOfDevices and GetDeviceName.

Since we will open the device in DeviceInfoLinux::GetDeviceName anyway, I think we should return the number of /dev/video* in DeviceInfoLinux::NumberOfDevices without trying to open it. Otherwise the DeviceInfoLinux::NumberOfDevices should return more information like which /dev/video* is valid which is not.

bool found = false;
for (int i = 0; i < vie_capture->NumberOfCaptureDevices(); ++i) {
  if (vie_capture->GetCaptureDevice(i, ...) == 0) {
    found = true;
    break;
  }
}
Review URL: http://webrtc-codereview.appspot.com/148004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@635 4adac7df-926f-26a2-2b94-8c16560cd09d
---
 .../main/source/Linux/device_info_linux.cc    | 32 +++++++++++++------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/src/modules/video_capture/main/source/Linux/device_info_linux.cc b/src/modules/video_capture/main/source/Linux/device_info_linux.cc
index dbdd582617..013b8f9058 100644
--- a/src/modules/video_capture/main/source/Linux/device_info_linux.cc
+++ b/src/modules/video_capture/main/source/Linux/device_info_linux.cc
@@ -80,7 +80,7 @@ WebRtc_UWord32 DeviceInfoLinux::NumberOfDevices()
         sprintf(device, "/dev/video%d", n);
         if (stat(device, &s) == 0) //check validity of path
         {
-            if ((fd = open(device, O_RDONLY)) > 0 || errno == EBUSY)
+            if ((fd = open(device, O_RDONLY)) != -1)
             {
                 close(fd);
                 count++;
@@ -102,22 +102,34 @@ WebRtc_Word32 DeviceInfoLinux::GetDeviceName(
 {
     WEBRTC_TRACE(webrtc::kTraceApiCall, webrtc::kTraceVideoCapture, _id, "%s", __FUNCTION__);
 
+    // Travel through /dev/video [0-63]
+    WebRtc_UWord32 count = 0;
     char device[20];
-    sprintf(device, "/dev/video%d", (int) deviceNumber);
     int fd = -1;
-
-    // open video device in RDONLY mode
-    struct stat s;
-    if (stat(device, &s) == 0)
+    bool found = false;
+    for (int n = 0; n < 64; n++)
     {
-        if ((fd = open(device, O_RDONLY)) < 0)
+        struct stat s;
+        sprintf(device, "/dev/video%d", n);
+        if (stat(device, &s) == 0)  // Check validity of path
         {
-            WEBRTC_TRACE(webrtc::kTraceError, webrtc::kTraceVideoCapture, _id,
-                       "error in opening video device. errno = %d", errno);
-            return -1;
+            if ((fd = open(device, O_RDONLY)) != -1)
+            {
+                if (count == deviceNumber) {
+                    // Found the device
+                    found = true;
+                    break;
+                } else {
+                    close(fd);
+                    count++;
+                }
+            }
         }
     }
 
+    if (!found)
+        return -1;
+
     // query device capabilities
     struct v4l2_capability cap;
     if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0)