diff --git a/device/device.go b/device/device.go index ab38da2..35aaa8b 100644 --- a/device/device.go +++ b/device/device.go @@ -2,6 +2,7 @@ package device import ( "context" + "errors" "fmt" "os" "reflect" @@ -27,7 +28,12 @@ type Device struct { // Open creates opens the underlying device at specified path for streaming. // It returns a *Device or an error if unable to open device. func Open(path string, options ...Option) (*Device, error) { - dev := &Device{path: path, config: config{}} + fd, err := v4l2.OpenDevice(path, sys.O_RDWR|sys.O_NONBLOCK, 0) + if err != nil { + return nil, fmt.Errorf("device open: %w", err) + } + + dev := &Device{path: path, config: config{}, fd: fd} // apply options if len(options) > 0 { for _, o := range options { @@ -35,18 +41,10 @@ func Open(path string, options ...Option) (*Device, error) { } } - file, err := os.OpenFile(path, sys.O_RDWR|sys.O_NONBLOCK, 0644) - //file, err := os.OpenFile(path, sys.O_RDWR, 0644) - if err != nil { - return nil, fmt.Errorf("device open: %w", err) - } - dev.file = file - dev.fd = file.Fd() - // get capability - cap, err := v4l2.GetCapability(file.Fd()) + cap, err := v4l2.GetCapability(dev.fd) if err != nil { - if err := file.Close(); err != nil { + if err := v4l2.CloseDevice(dev.fd); err != nil { return nil, fmt.Errorf("device %s: closing after failure: %s", path, err) } return nil, fmt.Errorf("device open: %s: %w", path, err) @@ -60,7 +58,7 @@ func Open(path string, options ...Option) (*Device, error) { // only supports streaming IO model right now if !dev.cap.IsStreamingSupported() { - return nil, fmt.Errorf("device open: only streaming IO is supported") + return nil, fmt.Errorf("device open: device does not support streamingIO") } switch { @@ -71,7 +69,7 @@ func Open(path string, options ...Option) (*Device, error) { case cap.IsVideoOutputSupported(): dev.bufType = v4l2.BufTypeVideoOutput default: - if err := file.Close(); err != nil { + if err := v4l2.CloseDevice(dev.fd); err != nil { return nil, fmt.Errorf("device open: %s: closing after failure: %s", path, err) } return nil, fmt.Errorf("device open: %s: %w", path, v4l2.ErrorUnsupportedFeature) @@ -81,30 +79,36 @@ func Open(path string, options ...Option) (*Device, error) { return nil, fmt.Errorf("device open: does not support buffer stream type") } - // ensures IOType is set - if reflect.ValueOf(dev.config.ioType).IsZero() { - dev.config.ioType = v4l2.IOTypeMMAP + // ensures IOType is set, only MemMap supported now + dev.config.ioType = v4l2.IOTypeMMAP + + // reset crop, only if cropping supported + if cropcap, err := v4l2.GetCropCapability(dev.fd, dev.bufType); err == nil { + if err := v4l2.SetCropRect(dev.fd, cropcap.DefaultRect); err != nil { + // ignore errors + } } // set pix format if !reflect.ValueOf(dev.config.pixFormat).IsZero() { if err := dev.SetPixFormat(dev.config.pixFormat); err != nil { - fmt.Errorf("device open: %s: set format: %w", path, err) + return nil, fmt.Errorf("device open: %s: set format: %w", path, err) } } else { - if dev.config.pixFormat, err = v4l2.GetPixFormat(dev.fd); err != nil { - fmt.Errorf("device open: %s: get pix format: %w", path, err) + dev.config.pixFormat, err = v4l2.GetPixFormat(dev.fd) + if err != nil { + return nil, fmt.Errorf("device open: %s: get default format: %w", path, err) } } // set fps if !reflect.ValueOf(dev.config.fps).IsZero() { if err := dev.SetFrameRate(dev.config.fps); err != nil { - fmt.Errorf("device open: %s: set fps: %w", path, err) + return nil, fmt.Errorf("device open: %s: set fps: %w", path, err) } } else { if dev.config.fps, err = dev.GetFrameRate(); err != nil { - fmt.Errorf("device open: %s: get fps: %w", path, err) + return nil, fmt.Errorf("device open: %s: get fps: %w", path, err) } } @@ -118,8 +122,7 @@ func (d *Device) Close() error { return err } } - - return d.file.Close() + return v4l2.CloseDevice(d.fd) } // Name returns the device name (or path) @@ -336,9 +339,12 @@ func (d *Device) Start(ctx context.Context) error { // allocate device buffers bufReq, err := v4l2.InitBuffers(d) if err != nil { - return fmt.Errorf("device: init buffers: %w", err) + return fmt.Errorf("device: requested buffer type not be supported: %w", err) } - d.config.bufSize = bufReq.Count // update with granted buf size + if bufReq.Count < 2 { + return fmt.Errorf("device: %s: issuficient buffer memory", d.path) + } + d.config.bufSize = bufReq.Count d.requestedBuf = bufReq // for each allocated device buf, map into local space @@ -346,14 +352,6 @@ func (d *Device) Start(ctx context.Context) error { return fmt.Errorf("device: make mapped buffers: %s", err) } - // Initial enqueue of buffers for capture - for i := 0; i < int(d.config.bufSize); i++ { - _, err := v4l2.QueueBuffer(d.fd, d.config.ioType, d.bufType, uint32(i)) - if err != nil { - return fmt.Errorf("device: initial buffer queueing: %w", err) - } - } - if err := d.startStreamLoop(ctx); err != nil { return fmt.Errorf("device: start stream loop: %s", err) } @@ -377,9 +375,20 @@ func (d *Device) Stop() error { return nil } +// startStreamLoop sets up the loop to run until context is cancelled, and returns immediately +// and report any errors. The loop runs in a separate goroutine and uses the sys.Select to trigger +// capture events. func (d *Device) startStreamLoop(ctx context.Context) error { + // Initial enqueue of buffers for capture + for i := 0; i < int(d.config.bufSize); i++ { + _, err := v4l2.QueueBuffer(d.fd, d.config.ioType, d.bufType, uint32(i)) + if err != nil { + return fmt.Errorf("device: buffer queueing: %w", err) + } + } + if err := v4l2.StreamOn(d); err != nil { - return fmt.Errorf("stream loop: stream on: %w", err) + return fmt.Errorf("device: stream on: %w", err) } go func() { @@ -394,10 +403,16 @@ func (d *Device) startStreamLoop(ctx context.Context) error { select { // handle stream capture (read from driver) case <-waitForRead: - //TODO add better error-handling, for now just panic - buff, err := d.prepareCaptureBuffer(fd, ioMemType, bufType) + buff, err := v4l2.DequeueBuffer(fd, ioMemType, bufType) if err != nil { - panic(fmt.Errorf("stream loop: capture buffer: %s", err).Error()) + if errors.Is(err, sys.EAGAIN) { + continue + } + panic(fmt.Sprintf("device: stream loop dequeue: %s", err)) + } + + if _, err := v4l2.QueueBuffer(fd, ioMemType, bufType, buff.Index); err != nil { + panic(fmt.Sprintf("device: stream loop queue: %s: buff: %#v", err, buff)) } d.output <- d.Buffers()[buff.Index][:buff.BytesUsed] @@ -411,19 +426,3 @@ func (d *Device) startStreamLoop(ctx context.Context) error { return nil } - -// prepareCaptureBuffer prepares a frame buffer for stream capture -func (d *Device) prepareCaptureBuffer(fd uintptr, ioType v4l2.IOType, bufType v4l2.BufType) (v4l2.Buffer, error) { - bufInfo, err := v4l2.DequeueBuffer(fd, ioType, bufType) - if err != nil { - return v4l2.Buffer{}, fmt.Errorf("capture buffer info: dequeue: %w", err) - } - - // requeue/clear used buffer, prepare for next read - if _, err := v4l2.QueueBuffer(fd, ioType, bufType, bufInfo.Index); err != nil { - return v4l2.Buffer{}, fmt.Errorf("capture buffer info: queue: %w", err) - } - - // return captured buffer info - return bufInfo, nil -} diff --git a/examples/capture0/capture0.go b/examples/capture0/capture0.go index 89ab9e4..b29caf0 100644 --- a/examples/capture0/capture0.go +++ b/examples/capture0/capture0.go @@ -19,7 +19,7 @@ func main() { // open device device, err := device.Open( devName, - device.WithPixFormat(v4l2.PixFormat{PixelFormat: v4l2.PixelFmtMPEG, Width: 640, Height: 480}), + device.WithPixFormat(v4l2.PixFormat{PixelFormat: v4l2.PixelFmtMJPEG, Width: 640, Height: 480, Field: v4l2.FieldInterlaced}), ) if err != nil { log.Fatalf("failed to open device: %s", err) diff --git a/examples/ccapture/README.md b/examples/ccapture/README.md new file mode 100644 index 0000000..a216b9b --- /dev/null +++ b/examples/ccapture/README.md @@ -0,0 +1,30 @@ +# V4L2 video capture example in C + +This an example in C showing a minimally required steps to capture video using V4L2. This is can be used to run tests on devices and compare results with the Go4VL code. + +## Build and run +On a Linux machine, run the following: + +``` +gcc -o capture capture.c +``` + +Run the program using: + +``` +./capture +``` + +Or, run `--help` to see available flags: + +``` +./capture --help +``` + +## Debugging with `strace` + +To view the ioctl calls made when running the capture program: + +``` +strace -o trace.log -e trace=ioctl ./capture +``` \ No newline at end of file diff --git a/examples/ccapture/capture.c b/examples/ccapture/capture.c new file mode 100644 index 0000000..3156635 --- /dev/null +++ b/examples/ccapture/capture.c @@ -0,0 +1,434 @@ +/* + * V4L2 video capture example + * Used to validate result from test devices. + * Based on https://git.linuxtv.org/v4l-utils.git/ + */ + +#include +#include +#include +#include + +#include /* getopt_long() */ + +#include /* low-level i/o */ +#include +#include +#include +#include +#include +#include +#include + +#include + +#define CLEAR(x) memset(&(x), 0, sizeof(x)) + +enum io_method { + IO_METHOD_MMAP, +}; + +struct buffer { + void *start; + size_t length; +}; + +static char *dev_name; +static enum io_method io = IO_METHOD_MMAP; +static int fd = -1; +struct buffer *buffers; +static unsigned int n_buffers; +static int out_buf; +static int force_format; +static int frame_count = 70; + +static void errno_exit(const char *s) +{ + fprintf(stderr, "%s error %d, %s\n", s, errno, strerror(errno)); + exit(EXIT_FAILURE); +} + +static int xioctl(int fh, unsigned long int request, void *arg) +{ + int r; + + do { + r = ioctl(fh, request, arg); + } while (-1 == r && EINTR == errno); + + return r; +} + +static void process_image(const void *p, int size) +{ + if (out_buf) + fwrite(p, size, 1, stdout); + + fflush(stderr); + fprintf(stderr, "."); + fflush(stdout); +} + +static int read_frame(void) +{ + struct v4l2_buffer buf; + unsigned int i; + + CLEAR(buf); + + buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + buf.memory = V4L2_MEMORY_MMAP; + + if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) { + switch (errno) { + case EAGAIN: + return 0; + + case EIO: + /* Could ignore EIO, see spec. */ + + /* fall through */ + + default: + errno_exit("VIDIOC_DQBUF"); + } + } + + assert(buf.index < n_buffers); + + process_image(buffers[buf.index].start, buf.bytesused); + + if (-1 == xioctl(fd, VIDIOC_QBUF, &buf)) + errno_exit("VIDIOC_QBUF"); + + return 1; +} + +static void mainloop(void) +{ + unsigned int count; + + count = frame_count; + + while (count-- > 0) { + for (;;) { + fd_set fds; + struct timeval tv; + int r; + + FD_ZERO(&fds); + FD_SET(fd, &fds); + + /* Timeout. */ + tv.tv_sec = 2; + tv.tv_usec = 0; + + r = select(fd + 1, &fds, NULL, NULL, &tv); + + if (-1 == r) { + if (EINTR == errno) + continue; + errno_exit("select"); + } + + if (0 == r) { + fprintf(stderr, "select timeout\n"); + exit(EXIT_FAILURE); + } + + if (read_frame()) + break; + /* EAGAIN - continue select loop. */ + } + } +} + +static void stop_capturing(void) +{ + enum v4l2_buf_type type; + + type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + if (-1 == xioctl(fd, VIDIOC_STREAMOFF, &type)) + errno_exit("VIDIOC_STREAMOFF"); + +} + +static void start_capturing(void) +{ + unsigned int i; + enum v4l2_buf_type type; + + + for (i = 0; i < n_buffers; ++i) { + struct v4l2_buffer buf; + + CLEAR(buf); + buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + buf.memory = V4L2_MEMORY_MMAP; + buf.index = i; + + if (-1 == xioctl(fd, VIDIOC_QBUF, &buf)) + errno_exit("VIDIOC_QBUF"); + } + type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + if (-1 == xioctl(fd, VIDIOC_STREAMON, &type)) + errno_exit("VIDIOC_STREAMON"); + +} + +static void uninit_device(void) +{ + unsigned int i; + for (i = 0; i < n_buffers; ++i) + if (-1 == munmap(buffers[i].start, buffers[i].length)) + errno_exit("munmap"); + + free(buffers); +} + +static void init_mmap(void) +{ + struct v4l2_requestbuffers req; + + CLEAR(req); + + req.count = 4; + req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + req.memory = V4L2_MEMORY_MMAP; + + if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) { + if (EINVAL == errno) { + fprintf(stderr, "%s does not support " + "memory mapping\n", dev_name); + exit(EXIT_FAILURE); + } else { + errno_exit("VIDIOC_REQBUFS"); + } + } + + if (req.count < 2) { + fprintf(stderr, "Insufficient buffer memory on %s\n", + dev_name); + exit(EXIT_FAILURE); + } + + buffers = calloc(req.count, sizeof(*buffers)); + + if (!buffers) { + fprintf(stderr, "Out of memory\n"); + exit(EXIT_FAILURE); + } + + for (n_buffers = 0; n_buffers < req.count; ++n_buffers) { + struct v4l2_buffer buf; + + CLEAR(buf); + + buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + buf.memory = V4L2_MEMORY_MMAP; + buf.index = n_buffers; + + if (-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf)) + errno_exit("VIDIOC_QUERYBUF"); + + buffers[n_buffers].length = buf.length; + buffers[n_buffers].start = + mmap(NULL /* start anywhere */, + buf.length, + PROT_READ | PROT_WRITE /* required */, + MAP_SHARED /* recommended */, + fd, buf.m.offset); + + if (MAP_FAILED == buffers[n_buffers].start) + errno_exit("mmap"); + } +} + +static void init_device(void) +{ + struct v4l2_capability cap; + struct v4l2_cropcap cropcap; + struct v4l2_crop crop; + struct v4l2_format fmt; + + if (-1 == xioctl(fd, VIDIOC_QUERYCAP, &cap)) { + if (EINVAL == errno) { + fprintf(stderr, "%s is no V4L2 device\n", + dev_name); + exit(EXIT_FAILURE); + } else { + errno_exit("VIDIOC_QUERYCAP"); + } + } + + if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) { + fprintf(stderr, "%s is no video capture device\n", + dev_name); + exit(EXIT_FAILURE); + } + + if (!(cap.capabilities & V4L2_CAP_STREAMING)) { + fprintf(stderr, "%s does not support streaming i/o\n", dev_name); + exit(EXIT_FAILURE); + } + + + /* Select video input, video standard and tune here. */ + CLEAR(cropcap); + + cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + + if (0 == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) { + crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + crop.c = cropcap.defrect; /* reset to default */ + + if (-1 == xioctl(fd, VIDIOC_S_CROP, &crop)) { + switch (errno) { + case EINVAL: + /* Cropping not supported. */ + break; + default: + /* Errors ignored. */ + break; + } + } + } else { + /* Errors ignored. */ + } + + + CLEAR(fmt); + + fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; + if (force_format) { + fmt.fmt.pix.width = 640; + fmt.fmt.pix.height = 480; + fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV; + fmt.fmt.pix.field = V4L2_FIELD_INTERLACED; + + if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt)) + errno_exit("VIDIOC_S_FMT"); + + /* Note VIDIOC_S_FMT may change width and height. */ + } else { + /* Preserve original settings as set by v4l2-ctl for example */ + if (-1 == xioctl(fd, VIDIOC_G_FMT, &fmt)) + errno_exit("VIDIOC_G_FMT"); + } + + init_mmap(); +} + +static void close_device(void) +{ + if (-1 == close(fd)) + errno_exit("close"); + + fd = -1; +} + +static void open_device(void) +{ + struct stat st; + + if (-1 == stat(dev_name, &st)) { + fprintf(stderr, "Cannot identify '%s': %d, %s\n", + dev_name, errno, strerror(errno)); + exit(EXIT_FAILURE); + } + + if (!S_ISCHR(st.st_mode)) { + fprintf(stderr, "%s is no device\n", dev_name); + exit(EXIT_FAILURE); + } + + fd = open(dev_name, O_RDWR /* required */ | O_NONBLOCK, 0); + + if (-1 == fd) { + fprintf(stderr, "Cannot open '%s': %d, %s\n", + dev_name, errno, strerror(errno)); + exit(EXIT_FAILURE); + } +} + +static void usage(FILE *fp, int argc, char **argv) +{ + fprintf(fp, + "Usage: %s [options]\n\n" + "Version 1.3\n" + "Options:\n" + "-d | --device name Video device name [%s]\n" + "-h | --help Print this message\n" + "-o | --output Outputs stream to stdout\n" + "-f | --format Force format to 640x480 YUYV\n" + "-c | --count Number of frames to grab [%i]\n" + "", + argv[0], dev_name, frame_count); +} + +static const char short_options[] = "d:hmruofc:"; + +static const struct option +long_options[] = { + { "device", required_argument, NULL, 'd' }, + { "help", no_argument, NULL, 'h' }, + { "mmap", no_argument, NULL, 'm' }, + { "output", no_argument, NULL, 'o' }, + { "format", no_argument, NULL, 'f' }, + { "count", required_argument, NULL, 'c' }, + { 0, 0, 0, 0 } +}; + +int main(int argc, char **argv) +{ + dev_name = "/dev/video0"; + + for (;;) { + int idx; + int c; + + c = getopt_long(argc, argv, + short_options, long_options, &idx); + + if (-1 == c) + break; + + switch (c) { + case 0: /* getopt_long() flag */ + break; + + case 'd': + dev_name = optarg; + break; + + case 'h': + usage(stdout, argc, argv); + exit(EXIT_SUCCESS); + + case 'o': + out_buf++; + break; + + case 'c': + errno = 0; + frame_count = strtol(optarg, NULL, 0); + if (errno) + errno_exit(optarg); + break; + + default: + usage(stderr, argc, argv); + exit(EXIT_FAILURE); + } + } + + open_device(); + init_device(); + start_capturing(); + mainloop(); + stop_capturing(); + uninit_device(); + close_device(); + fprintf(stderr, "\n"); + return 0; +} \ No newline at end of file diff --git a/v4l2/errors.go b/v4l2/errors.go index 7b454a1..7584001 100644 --- a/v4l2/errors.go +++ b/v4l2/errors.go @@ -12,12 +12,15 @@ var ( ErrorTimeout = errors.New("timeout error") ErrorUnsupported = errors.New("unsupported error") ErrorUnsupportedFeature = errors.New("feature unsupported error") + ErrorInterrupted = errors.New("interrupted") ) func parseErrorType(errno sys.Errno) error { switch errno { case sys.EBADF, sys.ENOMEM, sys.ENODEV, sys.EIO, sys.ENXIO, sys.EFAULT: // structural, terminal return ErrorSystem + case sys.EINTR: + return ErrorInterrupted case sys.EINVAL: // bad argument return ErrorBadArgument case sys.ENOTTY: // unsupported diff --git a/v4l2/ioctl.go b/v4l2/ioctl.go deleted file mode 100644 index d49527c..0000000 --- a/v4l2/ioctl.go +++ /dev/null @@ -1,34 +0,0 @@ -package v4l2 - -import ( - sys "golang.org/x/sys/unix" -) - -// ioctl is a wrapper for Syscall(SYS_IOCTL) -func ioctl(fd, req, arg uintptr) (err sys.Errno) { - if _, _, errno := sys.Syscall(sys.SYS_IOCTL, fd, req, arg); errno != 0 { - if errno != 0 { - err = errno - return - } - } - return 0 -} - -// send sends a request to the kernel (via ioctl syscall) -func send(fd, req, arg uintptr) error { - errno := ioctl(fd, req, arg) - if errno == 0 { - return nil - } - parsedErr := parseErrorType(errno) - switch parsedErr { - case ErrorUnsupported, ErrorSystem, ErrorBadArgument: - return parsedErr - case ErrorTimeout, ErrorTemporary: - // TODO add code for automatic retry/recovery - return errno - default: - return errno - } -} diff --git a/v4l2/streaming.go b/v4l2/streaming.go index fc58c34..6f9c2a3 100644 --- a/v4l2/streaming.go +++ b/v4l2/streaming.go @@ -140,7 +140,7 @@ func StreamOff(dev StreamingDevice) error { return nil } -// InitBuffers sends buffer allocation request to initialize buffer IO +// InitBuffers sends buffer allocation request (VIDIOC_REQBUFS) to initialize buffer IO // for video capture or video output when using either mem map, user pointer, or DMA buffers. // See https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/vidioc-reqbufs.html#vidioc-reqbufs func InitBuffers(dev StreamingDevice) (RequestBuffers, error) { @@ -153,7 +153,26 @@ func InitBuffers(dev StreamingDevice) (RequestBuffers, error) { req.memory = C.uint(dev.MemIOType()) if err := send(dev.Fd(), C.VIDIOC_REQBUFS, uintptr(unsafe.Pointer(&req))); err != nil { - return RequestBuffers{}, fmt.Errorf("request buffers: %w", err) + return RequestBuffers{}, fmt.Errorf("request buffers: %w: type not supported", err) + } + + return *(*RequestBuffers)(unsafe.Pointer(&req)), nil +} + +// ResetBuffers allocates a buffer of size 0 VIDIOC_REQBUFS(0) to free (or orphan) all +// buffers. Useful when shuttingdown the stream. +// See https://linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/vidioc-reqbufs.html +func ResetBuffers(dev StreamingDevice) (RequestBuffers, error) { + if dev.MemIOType() != IOTypeMMAP && dev.MemIOType() != IOTypeDMABuf { + return RequestBuffers{}, fmt.Errorf("reset buffers: %w", ErrorUnsupported) + } + var req C.struct_v4l2_requestbuffers + req.count = C.uint(0) + req._type = C.uint(dev.BufferType()) + req.memory = C.uint(dev.MemIOType()) + + if err := send(dev.Fd(), C.VIDIOC_REQBUFS, uintptr(unsafe.Pointer(&req))); err != nil { + return RequestBuffers{}, fmt.Errorf("reset buffers VIDIOC_REQBUFS(0): %w", err) } return *(*RequestBuffers)(unsafe.Pointer(&req)), nil @@ -168,7 +187,7 @@ func GetBuffer(dev StreamingDevice, index uint32) (Buffer, error) { v4l2Buf.index = C.uint(index) if err := send(dev.Fd(), C.VIDIOC_QUERYBUF, uintptr(unsafe.Pointer(&v4l2Buf))); err != nil { - return Buffer{}, fmt.Errorf("query buffer: %w", err) + return Buffer{}, fmt.Errorf("query buffer: type not supported: %w", err) } return makeBuffer(v4l2Buf), nil @@ -253,9 +272,9 @@ func DequeueBuffer(fd uintptr, ioType IOType, bufType BufType) (Buffer, error) { v4l2Buf._type = C.uint(bufType) v4l2Buf.memory = C.uint(ioType) - if err := send(fd, C.VIDIOC_DQBUF, uintptr(unsafe.Pointer(&v4l2Buf))); err != nil { - return Buffer{}, fmt.Errorf("buffer dequeue: %w", err) - + err := send(fd, C.VIDIOC_DQBUF, uintptr(unsafe.Pointer(&v4l2Buf))) + if err != nil { + return Buffer{}, fmt.Errorf("buffer dequeue: EGAIN: %w", err) } return makeBuffer(v4l2Buf), nil diff --git a/v4l2/streaming_loop.go b/v4l2/streaming_loop.go deleted file mode 100644 index 0d026f1..0000000 --- a/v4l2/streaming_loop.go +++ /dev/null @@ -1,28 +0,0 @@ -package v4l2 - -import ( - sys "golang.org/x/sys/unix" -) - -// WaitForRead returns a channel that can be used to be notified when -// a device's is ready to be read. -func WaitForRead(dev Device) <-chan struct{} { - sigChan := make(chan struct{}) - - go func(fd uintptr) { - defer close(sigChan) - var fdsRead sys.FdSet - fdsRead.Set(int(fd)) - for { - n, err := sys.Select(int(fd+1), &fdsRead, nil, nil, nil) - if n == -1 { - if err == sys.EINTR { - continue - } - } - sigChan <- struct{}{} - } - }(dev.Fd()) - - return sigChan -} diff --git a/v4l2/syscalls.go b/v4l2/syscalls.go new file mode 100644 index 0000000..5b0d33d --- /dev/null +++ b/v4l2/syscalls.go @@ -0,0 +1,110 @@ +package v4l2 + +import ( + "errors" + "fmt" + "io/fs" + "os" + + sys "golang.org/x/sys/unix" +) + +// OpenDevice offers a simpler file-open operation than the Go API's os.OpenFile (the Go API's +// operation causes some drivers to return busy). It also applies file validation prior to opening the device. +func OpenDevice(path string, flags int, mode uint32) (uintptr, error) { + fstat, err := os.Stat(path) + if err != nil { + return 0, fmt.Errorf("open device: %w", err) + } + + if (fstat.Mode() | fs.ModeCharDevice) == 0 { + return 0, fmt.Errorf("device open: %s: not character device", path) + } + + return openDev(path, flags, mode) +} + +// openDev offers a simpler file open operation than the Go API OpenFile. +// See https://cs.opensource.google/go/go/+/refs/tags/go1.19.1:src/os/file_unix.go;l=205 +func openDev(path string, flags int, mode uint32) (uintptr, error) { + var fd int + var err error + for { + fd, err = sys.Openat(sys.AT_FDCWD, path, flags, mode) + if err == nil { + break + } + + if errors.Is(err, ErrorInterrupted) { + continue //retry + } + + return 0, &os.PathError{Op: "open", Path: path, Err: err} + } + return uintptr(fd), nil +} + +// CloseDevice closes the device. +func CloseDevice(fd uintptr) error { + return closeDev(fd) +} + +func closeDev(fd uintptr) error { + return sys.Close(int(fd)) +} + +// ioctl is a wrapper for Syscall(SYS_IOCTL) +func ioctl(fd, req, arg uintptr) (err sys.Errno) { + for { + _, _, errno := sys.Syscall(sys.SYS_IOCTL, fd, req, arg) + switch errno { + case 0: + return 0 + case sys.EINTR: + continue // retry + default: + return errno + } + } +} + +// send sends a request to the kernel (via ioctl syscall) +func send(fd, req, arg uintptr) error { + errno := ioctl(fd, req, arg) + if errno == 0 { + return nil + } + parsedErr := parseErrorType(errno) + switch parsedErr { + case ErrorUnsupported, ErrorSystem, ErrorBadArgument: + return parsedErr + case ErrorTimeout, ErrorTemporary: + // TODO add code for automatic retry/recovery + return errno + default: + return errno + } +} + +// WaitForRead returns a channel that can be used to be notified when +// a device's is ready to be read. +func WaitForRead(dev Device) <-chan struct{} { + sigChan := make(chan struct{}) + + go func(fd uintptr) { + defer close(sigChan) + var fdsRead sys.FdSet + fdsRead.Set(int(fd)) + tv := sys.Timeval{Sec: 2, Usec: 0} + for { + _, errno := sys.Select(int(fd+1), &fdsRead, nil, nil, &tv) + if errno == sys.EINTR { + continue + } + + sigChan <- struct{}{} + } + }(dev.Fd()) + + return sigChan +}