libutil: Introduce util_sys and util_sys_get_dev_addr()

Many tools need to identify the device address of a given device. So
far, either the tool had its own implementation, or u2s_getbusid() was
used. Though, u2s_getbusid() was mainly designed for and used by the
DASD tools.

Introduce util_sys with a first function util_sys_get_dev_addr() which
provides a more universal way to identify the device address which is
not limited to one particular device type. The device address represents
either a busid (e.g. DASD), slot address (NVMe), H:C:T:L tuple (SCSI),
or other id types associated with a device.

Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

include/lib/util_sys.h

@@ -0,0 +1,17 @@
+/*
+ * @defgroup util_sys_h  util_sys: SysFS interface
+ * @{
+ * @brief Work with SysFS
+ *
+ * Copyright IBM Corp. 2019
+ *
+ * s390-tools is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See LICENSE for details.
+ */
+
+#ifndef LIB_UTIL_SYS_H
+#define LIB_UTIL_SYS_H
+
+int util_sys_get_dev_addr(const char *dev, char *addr);
+
+#endif /** LIB_UTIL_SYS_H @} */

libutil/Makefile

@@ -27,7 +27,8 @@ objects =	util_base.o \
 		util_part.o \
 		util_prg.o \
 		util_proc.o \
-		util_rec.o
+		util_rec.o \
+		util_sys.o
 
 util_base_example: util_base_example.o $(lib)
 util_panic_example: util_panic_example.o $(lib)

libutil/util_sys.c

@@ -0,0 +1,77 @@
+/*
+ * util - Utility function library
+ *
+ * SysFS helper functions
+ *
+ * Copyright IBM Corp. 2019
+ *
+ * s390-tools is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See LICENSE for details.
+ */
+
+#include <err.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "lib/util_path.h"
+#include "lib/util_sys.h"
+
+/* lstat() doesn't work for sysfs files, a fixed size is therefore inevitable */
+#define READLINK_SIZE	256
+
+/**
+ * Identify device address
+ *
+ * Identifying the device address with this function works for almost any
+ * character and block device (e.g. NVMe, SCSI, DASD, etc).
+ * The user must provide a buffer that is large enough for the desired device
+ * address to be read into \p addr.
+ *
+ * @param[in]	dev	Device node of interest
+ * @param[out]	addr	Identified device address
+ *
+ * @retval	 0	Success
+ * @retval	-1	Error while reading device information or
+ *			constructed path
+ */
+int util_sys_get_dev_addr(const char *dev, char *addr)
+{
+	char device[READLINK_SIZE], *result;
+	unsigned int maj, min;
+	struct stat s;
+	ssize_t len;
+	char *path;
+
+	if (stat(dev, &s) != 0)
+		return -1;
+
+	maj = major(s.st_rdev);
+	min = minor(s.st_rdev);
+
+	if (S_ISBLK(s.st_mode))
+		path = util_path_sysfs("dev/block/%u:%u/device", maj, min);
+	else if (S_ISCHR(s.st_mode))
+		path = util_path_sysfs("dev/char/%u:%u/device", maj, min);
+	else
+		return -1;
+
+	len = readlink(path, device, READLINK_SIZE - 1);
+	free(path);
+	if (len != -1)
+		device[len] = '\0';
+	else
+		return -1;
+
+	result = strrchr(device, '/');
+	if (result)
+		result++;
+	else
+		result = device;
+	strcpy(addr, result);
+
+	return 0;
+}