From 456c6bed0b9e0866c75f0f7c8579d5f4f3f3e966 Mon Sep 17 00:00:00 2001
From: "Dr. Joachim Schneider" <jesmx@hal.rhein-neckar.de>
Date: Sat, 6 Sep 2025 20:28:07 +0200
Subject: [PATCH 62/74] Re-enable mdadm --monitor ... for /dev/mdX

This fixes a regression introduced with
commit 84d969be8f6d ("Monitor: use snprintf to fill device name"):

With this fix

  mdadm --monitor --scan -1 -p <pgm>

is possible again for /dev/mdX without symlink in /dev/md/.

The bug can be reproduced by these steps:

(a) Create block devices for testing:

    $ dd if=/dev/zero of=/tmp/d0.bin bs=1M count=16
    $ dd if=/dev/zero of=/tmp/d1.bin bs=1M count=16

    $ losetup -f /tmp/d0.bin
    $ losetup -f /tmp/d1.bin
    $ losetup
    NAME       SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE   DIO LOG-SEC
    /dev/loop1         0      0         0  0 /tmp/d1.bin   0     512
    /dev/loop0         0      0         0  0 /tmp/d0.bin   0     512

(b) Create RAID-1 array '/dev/md0':

    $ mdadm --create /dev/md0 --level=1 --raid-devices=2  \
      /dev/loop0 /dev/loop1
    ...
    mdadm: array /dev/md0 started.

(c) Check:

    $ cat /proc/mdstat
    Personalities : [raid1]
    md0 : active raid1 loop1[1] loop0[0]
          15360 blocks super 1.2 [2/2] [UU]

    unused devices: <none>

(d) Create 'mdadm.conf':

    $ mdadm --detail --scan > /tmp/mdadm.conf
    $ cat /tmp/mdadm.conf
    ARRAY /dev/md0 metadata=1.2 UUID=c0280f55:9c32e4ff:34f85ea3:08d1331b

(e) Use this bash script ('/tmp/report') for 'mdadm --monitor':

    [[ $# -lt 2 ]] && exit 0

    problem="$1"
    shift
    array="$1"
    shift
    args="$*"

    echo "MD REPORT: ${problem} with ${array}: ${args}"

(f) Call mdamd in monitor mode:

    $ mdadm --monitor  -c /tmp/mdadm.conf --scan -1 -p /tmp/report

    Without the fix one gets this output:

      mdadm: DeviceDisappeared event detected on md device /dev/md/md0
      MD REPORT: DeviceDisappeared with /dev/md/md0:
      mdadm: NewArray event detected on md device /dev/md0
      MD REPORT: NewArray with /dev/md0:

    Only the output of the 'report'-script:

      $ mdadm  --monitor  -c /tmp/mdadm.conf --scan -1  \
        -p /tmp/report 2>/dev/null
      MD REPORT: DeviceDisappeared with /dev/md/md0:
      MD REPORT: NewArray with /dev/md0:

    With the fix no (warning) output is produced:

      $ /tmp/mdadm-FIXED  --monitor  -c /tmp/mdadm.conf --scan -1 \
        -p /tmp/report

Signed-off-by: Dr. Joachim Schneider <jesmx@hal.rhein-neckar.de>
---
 mdmonitor.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mdmonitor.c b/mdmonitor.c
index 22b0a818f9bd..314dafb4588b 100644
--- a/mdmonitor.c
+++ b/mdmonitor.c
@@ -256,8 +256,8 @@ int Monitor(struct mddev_dev *devlist,
 				continue;
 
 			st = xcalloc(1, sizeof *st);
-			snprintf(st->devname, MD_NAME_MAX + sizeof(DEV_MD_DIR), DEV_MD_DIR "%s",
-				 basename(mdlist->devname));
+			snprintf(st->devname, sizeof(st->devname), "%s%s",
+				 '/' == *mdlist->devname ? "" : DEV_MD_DIR, mdlist->devname);
 			if (!is_mddev(st->devname)) {
 				free(st);
 				continue;
-- 
2.50.1