From fa7a4dafa3d89b2e8787de102e4362e895d44b05 Mon Sep 17 00:00:00 2001
From: Stefan Haberland <sth@linux.ibm.com>
Date: Wed, 29 Jul 2020 11:24:55 +0200
Subject: [PATCH] libutil: add function to get base device for blockdevice
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Some operations are only possible on base devices not on partitions.
Add functions to determine if a given device is a partition or a base
device and to get the base device to a given partition.

Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
Reviewed-by: Philipp Rudo <prudo@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
---
 include/lib/util_sys.h |  5 +++
 libutil/util_sys.c     | 97 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 102 insertions(+)

diff --git a/include/lib/util_sys.h b/include/lib/util_sys.h
index e0f078b0..cf6f862a 100644
--- a/include/lib/util_sys.h
+++ b/include/lib/util_sys.h
@@ -12,6 +12,11 @@
 #ifndef LIB_UTIL_SYS_H
 #define LIB_UTIL_SYS_H
 
+#include <stdbool.h>
+
 int util_sys_get_dev_addr(const char *dev, char *addr);
+bool util_sys_dev_is_partition(dev_t dev);
+int util_sys_get_partnum(dev_t dev);
+int util_sys_get_base_dev(dev_t dev, dev_t *base_dev);
 
 #endif /** LIB_UTIL_SYS_H @} */
diff --git a/libutil/util_sys.c b/libutil/util_sys.c
index 024dac78..96f1548e 100644
--- a/libutil/util_sys.c
+++ b/libutil/util_sys.c
@@ -11,17 +11,114 @@
 
 #include <err.h>
 #include <errno.h>
+#include <linux/fs.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/sysmacros.h>
 #include <unistd.h>
 
+#include "lib/util_file.h"
+#include "lib/util_libc.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
+#define PAGE_SIZE	4096
+
+/**
+ * Return the partition number of a given partition.
+ *
+ * @param[in]	dev	Device node of interest
+ *
+ * @retval	int	Partition number of the device
+ * @retval	-1	Error when trying to read the partition number.
+ */
+int util_sys_get_partnum(dev_t dev)
+{
+	int partnum = -1;
+	char *path;
+
+	path = util_path_sysfs("dev/block/%u:%u/partition",
+			       major(dev), minor(dev));
+	if (util_file_read_i(&partnum, 10, path)) {
+		warnx("Could not read from path '%s'", path);
+		goto out;
+	}
+	if (partnum <= 0) {
+		warnx("Bad partition number in '%s'", path);
+		partnum = -1;
+		goto out;
+	}
+
+out:
+	free(path);
+	return partnum;
+}
+
+/**
+ * Determine if the given device is a partition.
+ *
+ * @param[in]	dev	Device node of interest
+ *
+ * @retval	true	Device is partition
+ * @retval	false	Device is not a partition
+ */
+bool util_sys_dev_is_partition(dev_t dev)
+{
+	bool is_part;
+	char *path;
+
+	path = util_path_sysfs("dev/block/%u:%u/partition",
+			       major(dev), minor(dev));
+	is_part = util_path_exists(path);
+	free(path);
+
+	return is_part;
+}
+
+/**
+ * Determine base device
+ *
+ * This function determines the base device \p base_dev of a given
+ * device \p dev. If \p dev is a base device, \p base_dev becomes \p dev.
+ *
+ * @param[in]	dev		Device node of interest
+ * @param[out]	base_dev	Identified base device
+ *
+ * @retval	 0		Success
+ * @retval	-1		Error while reading device information or
+ *				constructed path
+ */
+int util_sys_get_base_dev(dev_t dev, dev_t *base_dev)
+{
+	int base_major, base_minor;
+	char buf[PAGE_SIZE];
+	char *path;
+
+	/* check if the device already is a base device */
+	if (!util_sys_dev_is_partition(dev)) {
+		*base_dev = makedev(major(dev), minor(dev));
+		return 0;
+	}
+	path = util_path_sysfs("dev/block/%d:%d/../dev",
+			       major(dev), minor(dev));
+	if (util_file_read_line(buf, sizeof(buf), path)) {
+		warnx("Could not read from path '%s'", path);
+		free(path);
+		return -1;
+	}
+	free(path);
+	if (sscanf(buf, "%i:%i", &base_major, &base_minor) != 2) {
+		warn("Could not parse major:minor from string '%s'", buf);
+		return -1;
+	}
+	*base_dev = makedev(base_major, base_minor);
+
+	return 0;
+}
 
 /**
  * Identify device address