v4l2 access: use block mode for READWRITE devices

Also refactor common code with MMAP devices.
In block mode, the read buffer size is controlled. That ensures that
dequeued buffers do not get truncated.

modules/access/v4l2/access.c

@@ -49,8 +49,8 @@ struct access_sys_t
     vlc_v4l2_ctrl_t *controls;
 };
 
-static block_t *AccessRead( access_t * );
-static ssize_t AccessReadStream( access_t *, uint8_t *, size_t );
+static block_t *MMapBlock (access_t *);
+static block_t *ReadBlock (access_t *);
 static int AccessControl( access_t *, int, va_list );
 static int InitVideo(access_t *, int, uint32_t);
 
@@ -84,6 +84,7 @@ int AccessOpen( vlc_object_t *obj )
         goto error;
     }
 
+    sys->controls = ControlsInit (VLC_OBJECT(access), fd);
     access->pf_seek = NULL;
     access->pf_control = AccessControl;
     return VLC_SUCCESS;
@@ -105,8 +106,6 @@ int InitVideo (access_t *access, int fd, uint32_t caps)
     if (SetupInput (VLC_OBJECT(access), fd))
         return -1;
 
-    sys->controls = ControlsInit (VLC_OBJECT(access), fd);
-
     /* Try and find default resolution if not specified */
     struct v4l2_format fmt = { .type = V4L2_BUF_TYPE_VIDEO_CAPTURE };
     if (v4l2_ioctl (fd, VIDIOC_G_FMT, &fmt) < 0)
@@ -147,19 +146,20 @@ int InitVideo (access_t *access, int fd, uint32_t caps)
         sys->bufv = StartMmap (VLC_OBJECT(access), fd, &sys->bufc);
         if (sys->bufv == NULL)
             return -1;
-        access->pf_block = AccessRead;
+        access->pf_block = MMapBlock;
     }
     else if (caps & V4L2_CAP_READWRITE)
     {
         sys->blocksize = fmt.fmt.pix.sizeimage;
         sys->bufv = NULL;
-        access->pf_read = AccessReadStream;
+        access->pf_block = ReadBlock;
     }
     else
     {
-        msg_Err (access, "no supported I/O method");
+        msg_Err (access, "no supported capture method");
         return -1;
     }
+
     return 0;
 }
 
@@ -175,18 +175,35 @@ void AccessClose( vlc_object_t *obj )
     free( sys );
 }
 
-static block_t *AccessRead( access_t *access )
+/* Wait for data */
+static int AccessPoll (access_t *access)
 {
     access_sys_t *sys = access->p_sys;
+    struct pollfd ufd;
+
+    ufd.fd = sys->fd;
+    ufd.events = POLLIN;
+
+    switch (poll (&ufd, 1, 500))
+    {
+        case -1:
+            if (errno == EINTR)
+        case 0:
+            /* FIXME: kill this case (arbitrary timeout) */
+                return -1;
+            msg_Err (access, "poll error: %m");
+            access->info.b_eof = true;
+            return -1;
+    }
+    return 0;
+}
 
-    struct pollfd fd;
-    fd.fd = sys->fd;
-    fd.events = POLLIN;
-    fd.revents = 0;
 
-    /* Wait for data */
-    /* FIXME: kill timeout */
-    if( poll( &fd, 1, 500 ) <= 0 )
+static block_t *MMapBlock (access_t *access)
+{
+    access_sys_t *sys = access->p_sys;
+
+    if (AccessPoll (access))
         return NULL;
 
     block_t *block = GrabVideo (VLC_OBJECT(access), sys->fd, sys->bufv);
@@ -198,42 +215,29 @@ static block_t *AccessRead( access_t *access )
     return block;
 }
 
-static ssize_t AccessReadStream( access_t *access, uint8_t *buf, size_t len )
+static block_t *ReadBlock (access_t *access)
 {
     access_sys_t *sys = access->p_sys;
-    struct pollfd ufd;
-    int i_ret;
-
-    ufd.fd = sys->fd;
-    ufd.events = POLLIN;
 
-    if( access->info.b_eof )
-        return 0;
-
-    /* FIXME: kill timeout and vlc_object_alive() */
-    do
-    {
-        if( !vlc_object_alive(access) )
-            return 0;
+    if (AccessPoll (access))
+        return NULL;
 
-        ufd.revents = 0;
-    }
-    while( ( i_ret = poll( &ufd, 1, 500 ) ) == 0 );
+    block_t *block = block_Alloc (sys->blocksize);
+    if (unlikely(block == NULL))
+        return NULL;
 
-    if( i_ret < 0 )
+    ssize_t val = v4l2_read (sys->fd, block->p_buffer, block->i_buffer);
+    if (val < 0)
     {
-        if( errno != EINTR )
-            msg_Err( access, "poll error: %m" );
-        return -1;
-    }
-
-    i_ret = v4l2_read (sys->fd, buf, len);
-    if( i_ret == 0 )
+        block_Release (block);
+        msg_Err (access, "cannot read buffer: %m");
         access->info.b_eof = true;
-    else if( i_ret > 0 )
-        access->info.i_pos += i_ret;
+        return NULL;
+    }
 
-    return i_ret;
+    block->i_buffer = val;
+    access->info.i_pos += val;
+    return block;
 }
 
 static int AccessControl( access_t *access, int query, va_list args )