configfs: Provide configfs support

Parse a configuration name from the commandline, and utilise it to
identify the configfs configuration path.

Only the short-name (i.e. "uvc.1") is necessary to provide if there is
no ambiguity regarding the gadget, otherwise the gadget path should be
included ("g1/functions/uvc.1"). If the parameter is not provided then
the first function is utilised.

Legacy g_webcam is still supported, and the parameter will define the
UDC to match against if provided.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

1 files changed, 343 insertions, 0 deletions

diff --git a/configfs.c b/configfs.c
new file mode 100644
index 0000000..8d36a29
--- /dev/null
+++ b/configfs.c
@@ -0,0 +1,343 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * ConfigFS Gadget device handling
+ *
+ * Copyright (C) 2018 Kieran Bingham
+ *
+ * Contact: Kieran Bingham <kieran.bingham@ideasonboard.com>
+ */
+
+/* To provide basename and asprintf from the GNU library. */
+ #define _GNU_SOURCE
+
+#include <errno.h>
+#include <fcntl.h>
+#include <glob.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "configfs.h"
+
+/* -----------------------------------------------------------------------------
+ * Path handling and support
+ */
+
+static char *path_join(const char *dirname, const char *name)
+{
+	char *path;
+
+	asprintf(&path, "%s/%s", dirname, name);
+
+	return path;
+}
+
+static char *path_glob_first_match(const char *g)
+{
+	glob_t globbuf;
+	char *match = NULL;
+
+	glob(g, 0, NULL, &globbuf);
+
+	if (globbuf.gl_pathc)
+		match = strdup(globbuf.gl_pathv[0]);
+
+	globfree(&globbuf);
+
+	return match;
+}
+
+/* -----------------------------------------------------------------------------
+ * Attribute handling
+ */
+
+static int attribute_read(const char *path, const char *file, char *buf,
+			  unsigned int len)
+{
+	char *f;
+	int ret;
+	int fd;
+
+	f = path_join(path, file);
+	if (!f)
+		return -ENOMEM;
+
+	fd = open(f, O_RDONLY);
+	free(f);
+	if (fd == -1) {
+		printf("Failed to open attribute %s: %s\n", file,
+		       strerror(errno));
+		return -ENOENT;
+	}
+
+	ret = read(fd, buf, len - 1);
+	close(fd);
+
+	if (ret < 0) {
+		printf("Failed to read attribute %s: %s\n", file,
+		       strerror(errno));
+		return -ENODATA;
+	}
+
+	buf[ret] = '\0';
+
+	return 0;
+}
+
+static int attribute_read_uint(const char *path, const char *file,
+			       unsigned int *val)
+{
+	/* 4,294,967,295 */
+	char buf[11];
+	char *endptr;
+	int ret;
+
+	ret = attribute_read(path, file, buf, sizeof(buf));
+	if (ret)
+		return ret;
+
+	errno = 0;
+
+	/* base 0: Autodetect hex, octal, decimal. */
+	*val = strtoul(buf, &endptr, 0);
+	if (errno)
+		return -errno;
+
+	if (endptr == buf)
+		return -ENODATA;
+
+	return 0;
+}
+
+static char *attribute_read_str(const char *path, const char *file)
+{
+	char buf[1024];
+	char *p;
+	int ret;
+
+	ret = attribute_read(path, file, buf, sizeof(buf));
+	if (ret)
+		return NULL;
+
+	p = strrchr(buf, '\n');
+	if (p != buf)
+		*p = '\0';
+
+	return strdup(buf);
+}
+
+/* -----------------------------------------------------------------------------
+ * UDC parsing
+ */
+
+/*
+ * udc_find_video_device - Find the video device node for a UVC function
+ * @udc: The UDC name
+ * @function: The UVC function name
+ *
+ * This function finds the video device node corresponding to a UVC function as
+ * specified by a @function name and @udc name.
+ *
+ * The @function parameter specifies the name of the USB function, usually in
+ * the form "uvc.%u". If NULL the first function found will be used.
+ *
+ * The @udc parameter specifies the name of the UDC. If NULL any UDC that
+ * contains a function matching the @function name will be used.
+ *
+ * Return a pointer to a newly allocated string containing the video device node
+ * full path if the function is found. Otherwise return NULL. The returned
+ * pointer must be freed by the caller with a call to free().
+ */
+static char *udc_find_video_device(const char *udc, const char *function)
+{
+	char *vpath;
+	char *video = NULL;
+	glob_t globbuf;
+	unsigned int i;
+
+	asprintf(&vpath, "/sys/class/udc/%s/device/gadget/video4linux/video*",
+		 udc ? udc : "*");
+	if (!vpath)
+		return NULL;
+
+	glob(vpath, 0, NULL, &globbuf);
+	free(vpath);
+
+	for (i = 0; i < globbuf.gl_pathc; ++i) {
+		char *config;
+		bool match;
+
+		/* Match on the first if no search string. */
+		if (!function)
+			break;
+
+		config = attribute_read_str(globbuf.gl_pathv[i],
+					    "function_name");
+		match = strcmp(function, config) == 0;
+
+		free(config);
+
+		if (match)
+			break;
+	}
+
+	if (i < globbuf.gl_pathc) {
+		const char *v = basename(globbuf.gl_pathv[i]);
+
+		video = path_join("/dev", v);
+	}
+
+	globfree(&globbuf);
+
+	return video;
+}
+
+/* -----------------------------------------------------------------------------
+ * Legacy g_webcam support
+ */
+
+static const struct uvc_function_config g_webcam_config = {
+	.streaming_interval = 1,
+	.streaming_maxburst = 0,
+	.streaming_maxpacket = 1024,
+};
+
+static int parse_legacy_g_webcam(const char *udc,
+				 struct uvc_function_config *fc)
+{
+	*fc = g_webcam_config;
+
+	fc->video = udc_find_video_device(udc, NULL);
+
+	return fc->video ? 0 : -ENODEV;
+}
+
+/* -----------------------------------------------------------------------------
+ * ConfigFS support
+ */
+
+/*
+ * configfs_find_uvc_function - Find the ConfigFS full path for a UVC function
+ * @function: The UVC function name
+ *
+ * Return a pointer to a newly allocated string containing the full ConfigFS
+ * path to the function if the function is found. Otherwise return NULL. The
+ * returned pointer must be freed by the caller with a call to free().
+ */
+static char *configfs_find_uvc_function(const char *function)
+{
+	const char *target = function ? function : "*";
+	const char *root;
+	char *func_path;
+	char *path;
+
+	/*
+	 * The function description can be provided as a path from the
+	 * usb_gadget root "g1/functions/uvc.0", or if there is no ambiguity
+	 * over the gadget name, a shortcut "uvc.0" can be provided.
+	 */
+	if (!strchr(target, '/'))
+		root = "/sys/kernel/config/usb_gadget/*/functions";
+	else
+		root = "/sys/kernel/config/usb_gadget";
+
+	path = path_join(root, target);
+
+	func_path = path_glob_first_match(path);
+	free(path);
+
+	return func_path;
+}
+
+/*
+ * configfs_free_uvc_function - Free a uvc_function_config object
+ * @fc: The uvc_function_config to be freed
+ *
+ * Free the given @fc function previously allocated by a call to
+ * configfs_parse_uvc_function().
+ */
+void configfs_free_uvc_function(struct uvc_function_config *fc)
+{
+	free(fc->udc);
+	free(fc->video);
+
+	free(fc);
+}
+
+/*
+ * configfs_parse_uvc_function - Parse a UVC function configuration in ConfigFS
+ * @function: The function name
+ *
+ * This function locates and parse the configuration of a UVC function in
+ * ConfigFS as specified by the @function name argument. The function name can
+ * be fully qualified with a gadget name (e.g. "g%u/functions/uvc.%u"), or as a
+ * shortcut can be an unqualified function name (e.g. "uvc.%u"). When the
+ * function name is unqualified, the first function matching the name in any
+ * UDC will be returned.
+ *
+ * Return a pointer to a newly allocated UVC function configuration structure
+ * that contains configuration parameters for the function, if the function is
+ * found. Otherwise return NULL. The returned pointer must be freed by the
+ * caller with a call to free().
+ */
+struct uvc_function_config *configfs_parse_uvc_function(const char *function)
+{
+	struct uvc_function_config *fc;
+	char *fpath;
+	int ret = 0;
+
+	fc = malloc(sizeof *fc);
+	if (fc == NULL)
+		return NULL;
+
+	memset(fc, 0, sizeof *fc);
+
+	/* Find the function in ConfigFS. */
+	fpath = configfs_find_uvc_function(function);
+	if (!fpath) {
+		/*
+		 * If the function can't be found attempt legacy parsing to
+		 * support the g_webcam gadget. The function parameter contains
+		 * a UDC name in that case.
+		 */
+		ret = parse_legacy_g_webcam(function, fc);
+		if (ret) {
+			configfs_free_uvc_function(fc);
+			fc = NULL;
+		}
+
+		return fc;
+	}
+
+	/*
+	 * Parse the function configuration. Remove the gadget name qualifier
+	 * from the function name, if any.
+	 */
+	if (function)
+		function = basename(function);
+
+	fc->udc = attribute_read_str(fpath, "../../UDC");
+	fc->video = udc_find_video_device(fc->udc, function);
+	if (!fc->video)
+		ret = -ENODEV;
+
+	ret = ret ? : attribute_read_uint(fpath, "streaming_interval",
+					  &fc->streaming_interval);
+
+	ret = ret ? : attribute_read_uint(fpath, "streaming_maxburst",
+					  &fc->streaming_maxburst);
+
+	ret = ret ? : attribute_read_uint(fpath, "streaming_maxpacket",
+					  &fc->streaming_maxpacket);
+
+	if (ret) {
+		configfs_free_uvc_function(fc);
+		fc = NULL;
+	}
+
+	free(fpath);
+
+	return fc;
+}