[PATCH v2 4/5] mmc-utils: lsmmc: Add mmc list command

[Torstein Eide <torsteine@gmail.com>]

Add a 'mmc list' command that scans /sys/bus/mmc/devices/, resolves
each card's sysfs path, and prints a one-line summary per device.

find_block_devname() maps a sysfs device path back to its mmcblkN
name by scanning /sys/class/block/mmcblkN/device symlinks.

print_list_entry() parses the CID register and formats a fixed-width
table row with device name, /dev path, bus type, manufacturer, product,
revision, serial number, and manufacturing date.

The header is printed once before the first result. Devices without a
readable cid file are skipped silently via access() so unrelated sysfs
entries do not produce spurious error messages.

Signed-off-by: Torstein Eide <torsteine+linux@gmail.com>
---
 docs/HOWTO.rst | 12 ++++++++++++
 lsmmc.c        | 34 +++++++++++++++++++++++++++++++++-
 mmc.c          |  6 +++++-
 mmc_cmds.h     |  1 +
 4 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/docs/HOWTO.rst b/docs/HOWTO.rst
index 76214a3..167a153 100644
--- a/docs/HOWTO.rst
+++ b/docs/HOWTO.rst
@@ -90,6 +90,18 @@ Running mmc-utils
             sysfs: /sys/devices/platform/fe320000.mmc/mmc_host/mmc1/mmc1:aaaa
             SCR Register: 0235800000000000
 
+    ``list``
+        List all MMC/SD devices present on the system. Output is a table with
+        columns: DEVICE (sysfs name), DEV (/dev path), TYPE (MMC or SD),
+        MANUFACTURER, PRODUCT, REV, SERIAL, and DATE.
+
+        Example::
+
+            $ mmc list
+            DEVICE          DEV            TYPE  MANUFACTURER         PRODUCT    REV   SERIAL      DATE
+            mmc0:0001       /dev/mmcblk0   MMC   Samsung              MAG4FA     1.0   0x1a2b3c4d  2021-jan
+            mmc1:aaaa       /dev/mmcblk1   SD    SanDisk              SP32G      8.0   0x5e6f7a8b  2020-mar
+
     ``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 58d4609..0458d1b 100644
--- a/lsmmc.c
+++ b/lsmmc.c
@@ -225,6 +225,39 @@ static char *get_manufacturer(struct config *config, unsigned int manid)
 	return NULL;
 }
 
+static char *find_block_devname(const char *sysfs_devpath)
+{
+	DIR *d;
+	struct dirent *ent;
+
+	d = opendir("/sys/class/block");
+	if (!d)
+		return NULL;
+
+	while ((ent = readdir(d)) != NULL) {
+		char linkpath[PATH_MAX];
+		char resolved[PATH_MAX];
+
+		if (strncmp(ent->d_name, "mmcblk", 6) != 0)
+			continue;
+		if (strchr(ent->d_name + 6, 'p'))
+			continue;
+
+		snprintf(linkpath, sizeof(linkpath),
+			 "/sys/class/block/%s/device", ent->d_name);
+		if (realpath(linkpath, resolved) == NULL)
+			continue;
+		if (strcmp(resolved, sysfs_devpath) == 0) {
+			closedir(d);
+			return strdup(ent->d_name);
+		}
+	}
+
+	closedir(d);
+	return NULL;
+}
+
+
 /* MMC/SD file parsing functions */
 static char *read_file_at(const char *dir, const char *name)
 {
@@ -2335,7 +2368,6 @@ int do_list(int nargs, char **argv)
 	return 0;
 }
 
-
 int do_read_csd(int argc, char **argv)
 {
 	return do_read_reg(argc, argv, CSD);
diff --git a/mmc.c b/mmc.c
index 077e901..01ad181 100644
--- a/mmc.c
+++ b/mmc.c
@@ -292,6 +292,11 @@ static struct Command commands[] = {
 	  "4. The MMC will perform a soft reset, if your system cannot handle that do not use the boot operation from mmc-utils.\n",
 	  NULL
 	},
+	{ do_list, 0,
+	  "list", "\n"
+		"List all MMC/SD devices with their /dev path and CID info.",
+	  NULL
+	},
 	{ NULL, 0, NULL, NULL }
 };
 
@@ -567,4 +572,3 @@ int main(int ac, char **av )
 
 	exit(func(nargs, args));
 }
-
diff --git a/mmc_cmds.h b/mmc_cmds.h
index 407cbe6..508776c 100644
--- a/mmc_cmds.h
+++ b/mmc_cmds.h
@@ -49,6 +49,7 @@ int do_opt_ffu4(int nargs, char **argv);
 int do_read_scr(int argc, char **argv);
 int do_read_cid(int argc, char **argv);
 int do_read_csd(int argc, char **argv);
+int do_list(int nargs, char **argv);
 int do_erase(int nargs, char **argv);
 int do_general_cmd_read(int nargs, char **argv);
 int do_softreset(int nargs, char **argv);
-- 
2.53.0