lib: Add simple sysfs accessors

igt_sysfs_set() for setting an attribute via sysfs, igt_sysfs_get() for
reading.

v2: Lots of little bugs in igt_sysfs_get()
v3: Pass device to open, stop assuming Intel rules.
v4: Test opening and reading!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 196 insertions, 0 deletions

diff --git a/lib/igt_sysfs.c b/lib/igt_sysfs.c
new file mode 100644
index 00000000..1b31d7af
--- /dev/null
+++ b/lib/igt_sysfs.c
@@ -0,0 +1,196 @@
+/*
+ * Copyright © 2016 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#include <inttypes.h>
+#include <sys/stat.h>
+#include <sys/mount.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <i915_drm.h>
+
+#include "igt_sysfs.h"
+
+static int readN(int fd, char *buf, int len)
+{
+	int total = 0;
+	do {
+		int ret = read(fd, buf + total, len - total);
+		if (ret < 0 && (errno == EINTR || errno == EAGAIN))
+			continue;
+
+		if (ret <= 0)
+			return total ?: ret;
+
+		total += ret;
+	} while (1);
+}
+
+static int writeN(int fd, const char *buf, int len)
+{
+	int total = 0;
+	do {
+		int ret = write(fd, buf + total, len - total);
+		if (ret < 0 && (errno == EINTR || errno == EAGAIN))
+			continue;
+
+		if (ret <= 0)
+			return total ?: ret;
+
+		total += ret;
+	} while (1);
+}
+
+/**
+ * igt_sysfs_open:
+ * @device: fd of the device (or -1 to default to Intel)
+ *
+ * This opens the sysfs directory corresponding to device for use
+ * with igt_sysfs_set() and igt_sysfs_get().
+ *
+ * Returns:
+ * The directory fd, or -1 on failure.
+ */
+int igt_sysfs_open(int fd, int *idx)
+{
+	char path[80];
+	struct stat st;
+
+	if (fd != -1 && (fstat(fd, &st) || !S_ISCHR(st.st_mode)))
+		return -1;
+
+	for (int n = 0; n < 16; n++) {
+		int len = sprintf(path, "/sys/class/drm/card%d", n);
+		if (fd != -1) {
+			FILE *file;
+			int ret, maj, min;
+
+			sprintf(path + len, "/dev");
+			file = fopen(path, "r");
+			if (!file)
+				continue;
+
+			ret = fscanf(file, "%d:%d", &maj, &min);
+			fclose(file);
+
+			if (ret != 2 ||
+			    major(st.st_rdev) != maj ||
+			    minor(st.st_rdev) != min)
+				continue;
+		} else {
+			/* Bleh. Search for intel */
+			sprintf(path + len, "/error");
+			if (stat(path, &st))
+				continue;
+		}
+
+		path[len] = '\0';
+		if (idx)
+			*idx = n;
+		return open(path, O_RDONLY);
+	}
+
+	return -1;
+}
+
+/**
+ * igt_sysfs_set:
+ * @dir: directory for the device from igt_sysfs_open()
+ * @attr: name of the sysfs node to open
+ * @value: the string to write
+ *
+ * This writes the value to the sysfs file.
+ *
+ * Returns:
+ * True on success, false on failure.
+ */
+bool igt_sysfs_set(int dir, const char *attr, const char *value)
+{
+	int fd, len, ret;
+
+	fd = openat(dir, attr, O_WRONLY);
+	if (fd < 0)
+		return false;
+
+	len = strlen(value);
+	ret = writeN(fd, value, len);
+	close(fd);
+
+	return len == ret;
+}
+
+/**
+ * igt_sysfs_get:
+ * @dir: directory for the device from igt_sysfs_open()
+ * @attr: name of the sysfs node to open
+ *
+ * This reads the value from the sysfs file.
+ *
+ * Returns:
+ * A nul-terminated string, must be freed by caller after use, or NULL
+ * on failure.
+ */
+char *igt_sysfs_get(int dir, const char *attr)
+{
+	char *buf;
+	int len, offset, rem;
+	int ret, fd;
+
+	fd = openat(dir, attr, O_RDONLY);
+	if (fd < 0)
+		return NULL;
+
+	offset = 0;
+	len = 64;
+	rem = len - offset - 1;
+	buf = malloc(len);
+	if (!buf)
+		goto out;
+
+	while ((ret = readN(fd, buf + offset, rem)) == rem) {
+		char *newbuf;
+
+		newbuf = realloc(buf, 2*len);
+		if (!newbuf)
+			break;
+
+		len *= 2;
+		offset += ret;
+		rem = len - offset - 1;
+	}
+
+	if (ret != -1)
+		offset += ret;
+	buf[offset] = '\0';
+	while (offset > 0 && buf[offset-1] == '\n')
+		buf[--offset] = '\0';
+
+out:
+	close(fd);
+	return buf;
+}