[PATCH 2/4] mmc-utils: lsmmc: Accept /dev and /sys/block paths for register reads

[Torstein Eide <torsteine@gmail.com>]

Commands like 'cid read' previously required a raw sysfs device path
such as /sys/bus/mmc/devices/mmc0:0001/. Most users know their block
device as /dev/mmcblk0 or /sys/block/mmcblk0.

Add resolve_dev_path() which follows /sys/class/block/<dev>/device via
realpath() to reach the canonical sysfs device directory. Paths that
start with /dev/ or /sys/block/ are resolved automatically in
do_read_reg() before processing, and the resolved sysfs path is printed
so the caller can see which device was matched.

Signed-off-by: Torstein Eide <torsteine+linux@gmail.com>
---
 docs/HOWTO.rst | 59 ++++++++++++++++++++++++++++++++++++++++++--------
 lsmmc.c        | 42 +++++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+), 9 deletions(-)

diff --git a/docs/HOWTO.rst b/docs/HOWTO.rst
index 7a27a50..76214a3 100644
--- a/docs/HOWTO.rst
+++ b/docs/HOWTO.rst
@@ -35,19 +35,60 @@ Running mmc-utils
         Set user area write protection.
 
     ``csd read  [-h] [-v] [-b bus_type] [-r register]  <device path>``
-        Print CSD data from <device path>. The device path should specify the csd sysfs file directory.
-        if [bus_type] is passed (mmc or sd) the [register] content must be passed as well, and no need for device path.
-        it is useful for cases we are getting the register value without having the actual platform.
+        Print CSD data from <device path>. The device path may be one of the following:
+          - sysfs device directory  (/sys/devices/platform/fe310000.mmc/mmc_host/mmc0/mmc0:0001)
+          - device node (/dev/mmcblkN)
+          - sysfs block device entry (/sys/block/mmcblkN)
+        /dev/ and /sys/block/ paths are resolved to the sysfs device
+        directory automatically and the resolved path is printed.
+        If [-b bus_type] is passed (mmc or sd) the [-r register] content must
+        be passed as well, and no device path is required. Useful when the
+        register value is known without access to the actual hardware.
+
+        Example::
+
+            $ mmc csd read /dev/mmcblk0
+            sysfs: /sys/devices/platform/fe310000.mmc/mmc_host/mmc0/mmc0:0001
+            CSD Register: 00000000...
 
     ``cid read <device path>``
-        Print CID data from <device path>. The device path should specify the cid sysfs file directory.
-        if [bus_type] is passed (mmc or sd) the [register] content must be passed as well, and no need for device path.
-        it is useful for cases we are getting the register value without having the actual platform.
+        Print CID data from <device path>. The device path may be one of the following:
+          - sysfs device directory  (/sys/devices/platform/fe310000.mmc/mmc_host/mmc0/mmc0:0001)
+          - device node (/dev/mmcblkN)
+          - sysfs block device entry (/sys/block/mmcblkN)
+        /dev/ and /sys/block/ paths are resolved to the sysfs device
+        directory automatically and the resolved path is printed.
+        If [-b bus_type] is passed (mmc or sd) the [-r register] content must
+        be passed as well, and no device path is required. Useful when the
+        register value is known without access to the actual hardware.
+
+        Example::
+
+            $ mmc cid read /dev/mmcblk0
+            sysfs: /sys/devices/platform/fe310000.mmc/mmc_host/mmc0/mmc0:0001
+            Manufacturer ID: 0x15
+            OEM ID: 0x0100
+            Product name: MAG4FA
+            Product revision: 1.0
+            Serial number: 0x1a2b3c4d
+            Manufacturing date: 01/2021
 
     ``scr read <device path>``
-        Print SCR data from <device path>. The device path should specify the scr sysfs file directory.
-        if [bus_type] is passed (mmc or sd) the [register] content must be passed as well, and no need for device path.
-        it is useful for cases we are getting the register value without having the actual platform.
+        Print SCR data from <device path>. The device path may be one of the following:
+          - sysfs device directory  (/sys/devices/platform/fe320000.mmc/mmc_host/mmc1/mmc1:aaaa)
+          - device node (/dev/mmcblkN)
+          - sysfs block device entry (/sys/block/mmcblkN)
+        /dev/ and /sys/block/ paths are resolved to the sysfs device
+        directory automatically and the resolved path is printed.
+        If [-b bus_type] is passed (mmc or sd) the [-r register] content must
+        be passed as well, and no device path is required. Useful when the
+        register value is known without access to the actual hardware.
+
+        Example::
+
+            $ mmc scr read /dev/mmcblk1
+            sysfs: /sys/devices/platform/fe320000.mmc/mmc_host/mmc1/mmc1:aaaa
+            SCR Register: 0235800000000000
 
     ``ffu <image name> <device> [chunk-bytes]``
       Default mode.  Run Field Firmware Update with `<image name>` on `<device>`. `[chunk-bytes]` is optional and defaults to its max - 512k. Should be in decimal bytes and sector aligned.
diff --git a/lsmmc.c b/lsmmc.c
index 113f371..3149409 100644
--- a/lsmmc.c
+++ b/lsmmc.c
@@ -226,6 +226,33 @@ static const char *get_manufacturer(struct config *config, unsigned int manid)
 	return NULL;
 }
 
+static char *resolve_dev_path(const char *path)
+{
+	const char *devname = strrchr(path, '/');
+	char syspath[PATH_MAX];
+	char *resolved;
+
+	devname = devname ? devname + 1 : path;
+	if (*devname == '\0')
+		return NULL;
+
+	if (snprintf(syspath, sizeof(syspath), "/sys/class/block/%s/device",
+		     devname) >= PATH_MAX)
+		return NULL;
+
+	resolved = malloc(PATH_MAX);
+	if (!resolved)
+		return NULL;
+
+	if (realpath(syspath, resolved) == NULL) {
+		fprintf(stderr, "Cannot resolve '%s': %s\n", path, strerror(errno));
+		free(resolved);
+		return NULL;
+	}
+
+	return resolved;
+}
+
 /* MMC/SD file parsing functions */
 static char *read_file(char *name)
 {
@@ -2151,6 +2178,21 @@ static int do_read_reg(int argc, char **argv, enum REG_TYPE reg)
 	if (ret)
 		return ret;
 
+	if (cfg.dir &&
+	    (strncmp(cfg.dir, "/dev/", 5) == 0 ||
+	     strncmp(cfg.dir, "/sys/block/", 11) == 0)) {
+		char *sysfs = resolve_dev_path(cfg.dir);
+
+		if (!sysfs) {
+			free(cfg.dir);
+			return -1;
+		}
+
+		free(cfg.dir);
+		cfg.dir = sysfs;
+		printf("sysfs: %s\n", cfg.dir);
+	}
+
 	if (cfg.dir) {
 		ret = process_dir(&cfg, reg);
 		free(cfg.dir);
-- 
2.53.0