[PATCH v3 2/4] util: Introduce read_file() and read_file_long() function

[Yumei Huang <yuhuang@redhat.com>]

Signed-off-by: Yumei Huang <yuhuang@redhat.com>
---
 util.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 util.h |  2 ++
 2 files changed, 94 insertions(+)

diff --git a/util.c b/util.c
index c492f90..d331f08 100644
--- a/util.c
+++ b/util.c
@@ -579,6 +579,98 @@ int write_file(const char *path, const char *buf)
 	return len == 0 ? 0 : -1;
 }
 
+/**
+ * read_file() - Read contents of file into a buffer
+ * @path:	File to read
+ * @buf:	Buffer to store file contents
+ * @buf_size:	Size of buffer
+ *
+ * Return: number of bytes read on success, -1 on any error, -2 on truncation
+*/
+int read_file(const char *path, char *buf, size_t buf_size)
+{
+	int fd = open(path, O_RDONLY | O_CLOEXEC);
+	size_t total_read = 0;
+	ssize_t rc;
+	bool truncated = false;
+
+	if (fd < 0) {
+		warn_perror("Could not open %s", path);
+		return -1;
+	}
+
+	while (total_read < buf_size - 1) {
+		rc = read(fd, buf + total_read, buf_size - 1 - total_read);
+
+		if (rc < 0 ) {
+			warn_perror("Couldn't read from %s", path);
+			close(fd);
+			return -1;
+		}
+
+		if (rc == 0) {
+			break;
+		}
+
+		total_read += rc;
+
+		if (total_read == buf_size - 1) {
+			char test_byte;
+			rc = read(fd, &test_byte, 1);
+			if (rc >0) {
+				truncated = true;
+				warn_perror("File %s truncated, buffer too small", path);
+			}
+		}
+	}
+
+	close(fd);
+
+	if (total_read < buf_size){
+		buf[total_read] = '\0';
+	}
+
+	return truncated ? -2 : (int)total_read;
+}
+
+/**
+ * read_file_long() - Read a long integer value from a file
+ * @path: Path to the sysctl file
+ * @fallback: Default value if file can't be read
+ *
+ * Return: Parameter value, fallback on failure
+*/
+long read_file_long(const char *path, long fallback)
+{
+        char buf[32];
+        char *end;
+        long value;
+        int bytes_read;
+
+        bytes_read = read_file(path, buf, sizeof(buf));
+        if (bytes_read < 0) {
+                debug("Unable to read %s", path);
+                return fallback;
+        }
+
+        if (bytes_read == 0) {
+                debug("Empty file %s", path);
+                return fallback;
+        }
+
+        errno = 0;
+        value = strtol(buf, &end, 10);
+        if (*end && *end != '\n') {
+                debug("Invalid format in %s", path);
+                return fallback;
+        }
+        if (errno || value < 0 || value > LONG_MAX) {
+                debug("Invalid value in %s: %ld", path, value);
+                return fallback;
+        }
+        return value;
+}
+
 #ifdef __ia64__
 /* Needed by do_clone() below: glibc doesn't export the prototype of __clone2(),
  * use the description from clone(2).
diff --git a/util.h b/util.h
index 22eaac5..e509bec 100644
--- a/util.h
+++ b/util.h
@@ -222,6 +222,8 @@ void pidfile_write(int fd, pid_t pid);
 int __daemon(int pidfile_fd, int devnull_fd);
 int fls(unsigned long x);
 int write_file(const char *path, const char *buf);
+int read_file(const char *path, char *buf, size_t buf_size);
+long read_file_long(const char *path, long fallback);
 int write_all_buf(int fd, const void *buf, size_t len);
 int write_remainder(int fd, const struct iovec *iov, size_t iovcnt, size_t skip);
 int read_all_buf(int fd, void *buf, size_t len);
-- 
2.47.0