MDEV-26042 Atomic write capability is not detected correctly

my_init_atomic_write(): Detect all forms of SSD, in case multiple
types of devices are installed in the same machine.
This was broken in commit ed008a7
and further in commit 70684af.

SAME_DEV(): Match block devices, ignoring partition numbers.

Let us use stat() instead of lstat(), in case someone has a symbolic
link in /dev.

Instead of reporting errors with perror(), let us use fprintf(stderr)
with the file name, the impact of the error, and the strerror(errno).
Because this code is specific to Linux, we may depend on the
GNU libc/uClibc/musl extension %m for strerror(errno).

mysys/my_atomic_writes.c

@@ -1,4 +1,4 @@
-/* Copyright (c) 2016, MariaDB Corporation
+/* Copyright (c) 2016, 2021, MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -24,6 +24,10 @@ my_bool has_shannon_atomic_write= 0, has_fusion_io_atomic_write= 0,
 
 #include <sys/ioctl.h>
 
+/* Linux seems to allow up to 15 partitions per block device.
+Partition number 0 is the whole block device. */
+# define SAME_DEV(fs_dev, blk_dev) \
+  (fs_dev == blk_dev) || ((fs_dev & ~15U) == blk_dev)
 
 /***********************************************************************
   FUSION_IO
@@ -115,9 +119,9 @@ static my_bool test_if_shannon_card_exists()
 
     sprintf(path, "/dev/df%c", dev_part);
 #ifdef TEST_SHANNON
-    if (lstat(path, &stat_buff) < 0)
+    if (stat(path, &stat_buff) < 0)
     {
-      printf("%s(): lstat failed.\n", __func__);
+      printf("%s(): stat %s failed.\n", __func__, path);
       break;
     }
 #endif
@@ -147,7 +151,7 @@ static my_bool test_if_shannon_card_exists()
     for (dev_no= 1 ; dev_no < 9 ; dev_no++)
     {
       sprintf(path, "/dev/df%c%d", dev_part, dev_no);
-      if (lstat(path, &stat_buff) < 0)
+      if (stat(path, &stat_buff) < 0)
         break;
 
       shannon_devices[shannon_found_devices].st_dev= stat_buff.st_rdev;
@@ -194,12 +198,13 @@ static my_bool shannon_dev_has_atomic_write(struct shannon_dev *dev,
     int fd= open(dev->dev_name, 0);
     if (fd < 0)
     {
-      perror("open() failed!");
+      fprintf(stderr, "Unable to determine if atomic writes are supported:"
+              " open(\"%s\"): %m\n", dev->dev_name);
       dev->atomic_size= 0;                      /* Don't try again */
       return FALSE;
     }
-     dev->atomic_size= ioctl(fd, SHANNON_IOCQATOMIC_SIZE);
-     close(fd);
+    dev->atomic_size= ioctl(fd, SHANNON_IOCQATOMIC_SIZE);
+    close(fd);
   }
 
 #ifdef TEST_SHANNON
@@ -248,7 +253,7 @@ static my_bool shannon_has_atomic_write(File file, int page_size)
 #ifdef TEST_SHANNON
     printf("%s(): st_rdev=0x%lx\n", __func__, (ulong) dev->st_dev);
 #endif
-    if (stat_buff.st_dev == dev->st_dev)
+    if (SAME_DEV(stat_buff.st_dev, dev->st_dev))
       return shannon_dev_has_atomic_write(dev, page_size);
  }
  return 0;
@@ -290,8 +295,7 @@ static my_bool test_if_sfx_card_exists()
 
     sprintf(sfx_devices[sfx_found_devices].dev_name, "/dev/sfdv%dn1",
             dev_num);
-    if (lstat(sfx_devices[sfx_found_devices].dev_name,
-                &stat_buff) < 0)
+    if (stat(sfx_devices[sfx_found_devices].dev_name, &stat_buff) < 0)
       break;
 
     sfx_devices[sfx_found_devices].st_dev= stat_buff.st_rdev;
@@ -316,13 +320,15 @@ static my_bool sfx_dev_has_atomic_write(struct sfx_dev *dev,
     int fd= open(dev->dev_name, 0);
     if (fd < 0)
     {
-      perror("open() failed!");
+      fprintf(stderr, "Unable to determine if atomic writes are supported:"
+              " open(\"%s\"): %m\n", dev->dev_name);
       dev->atomic_size= 0;                      /* Don't try again */
-      return FALSE;
     }
-
-    dev->atomic_size= ioctl(fd, SFX_GET_ATOMIC_SIZE);
-    close(fd);
+    else
+    {
+      dev->atomic_size= ioctl(fd, SFX_GET_ATOMIC_SIZE);
+      close(fd);
+    }
   }
 
   return (page_size <= dev->atomic_size);
@@ -346,16 +352,10 @@ static my_bool sfx_has_atomic_write(File file, int page_size)
   struct sfx_dev *dev;
   struct stat stat_buff;
 
-  if (fstat(file, &stat_buff) < 0)
-  {
-    return 0;
-  }
-
-  for (dev = sfx_devices; dev->st_dev; dev++)
-  {
-    if (stat_buff.st_dev == dev->st_dev)
-      return sfx_dev_has_atomic_write(dev, page_size);
-  }
+  if (fstat(file, &stat_buff) == 0)
+    for (dev= sfx_devices; dev->st_dev; dev++)
+      if (SAME_DEV(stat_buff.st_dev, dev->st_dev))
+        return sfx_dev_has_atomic_write(dev, page_size);
   return 0;
 }
 /***********************************************************************
@@ -369,10 +369,13 @@ static my_bool sfx_has_atomic_write(File file, int page_size)
 
 void my_init_atomic_write(void)
 {
-  if ((has_shannon_atomic_write=   test_if_shannon_card_exists()) ||
-      (has_fusion_io_atomic_write= test_if_fusion_io_card_exists()) ||
-      (has_sfx_atomic_write=       test_if_sfx_card_exists()))
-  my_may_have_atomic_write= 1;
+  has_shannon_atomic_write= test_if_shannon_card_exists();
+  has_fusion_io_atomic_write= test_if_fusion_io_card_exists();
+  has_sfx_atomic_write= test_if_sfx_card_exists();
+
+  my_may_have_atomic_write= has_shannon_atomic_write ||
+    has_fusion_io_atomic_write || has_sfx_atomic_write;
+
 #ifdef TEST_SHANNON
   printf("%s(): has_shannon_atomic_write=%d, my_may_have_atomic_write=%d\n",
           __func__,