Re: [PATCH] Cygwin: Add /dev/disk/by-label and /dev/disk/by-uuid symlinks

[Christian Franke <Christian.Franke@t-online.de>]

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Corinna Vinschen wrote:
> On Nov 17 18:53, Christian Franke wrote:
>> Corinna Vinschen wrote:
>>> ...
>>> I see.  Admittedly, I don't know how Linux handles this either.
>> A quick test on Debian 12 with by-label suggests that the last duplicate
>> wins. Also not very sophisticated :-)
> Given this is all controlled by rather simple udev rules, see
> /usr/lib/udev/rules.d/60-persistent-storage.rules, that's not
> really surprising.
>
>> IIRC in the past I've seen in another of these directories (by-id?) that
>> '#N' was appended if duplicates occur.
> I don't see anything like that in 60-persistent-storage.rules, though.
> It has been removed at one point, it seems.

A quick followup to mark duplicates and (more important) avoid leading 
spaces in NTFS serial number.


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From 1e212814cfb17579105ead4835410bd74dfb188a Mon Sep 17 00:00:00 2001
From: Christian Franke <christian.franke@t-online.de>
Date: Fri, 17 Nov 2023 21:20:26 +0100
Subject: [PATCH] Cygwin: /dev/disk: Mark duplicates, fix serial number format

Keep ranges of duplicate names and append '#N' to each name.
Add missing leading zeros to output format of NTFS serial number.
No longer ignore null volume serial numbers.

Signed-off-by: Christian Franke <christian.franke@t-online.de>
---
 winsup/cygwin/fhandler/dev_disk.cc | 38 ++++++++++++++----------------
 1 file changed, 18 insertions(+), 20 deletions(-)

diff --git a/winsup/cygwin/fhandler/dev_disk.cc b/winsup/cygwin/fhandler/dev_disk.cc
index 016b4c7bc..131ffd935 100644
--- a/winsup/cygwin/fhandler/dev_disk.cc
+++ b/winsup/cygwin/fhandler/dev_disk.cc
@@ -64,10 +64,12 @@ sanitize_label_string (WCHAR *s)
   /* Linux does not skip leading spaces. */
   return sanitize_string (s, L'\0', L' ', L'_', [] (WCHAR c) -> bool
     {
-      /* Labels may contain characters not allowed in filenames.
-	 Linux replaces spaces with \x20 which is not an option here. */
+      /* Labels may contain characters not allowed in filenames.  Also
+         replace '#' to avoid that duplicate markers introduce new
+	 duplicates.  Linux replaces spaces with \x20 which is not an
+	 option here. */
       return !((0 <= c && c <= L' ') || c == L':' || c == L'/' || c == L'\\'
-	      || c == L'"');
+	      || c == L'#' || c == L'"');
     }
   );
 }
@@ -304,11 +306,10 @@ partition_to_label_or_uuid(bool uuid, const UNICODE_STRING *drive_uname,
   const NTFS_VOLUME_DATA_BUFFER *nvdb =
     reinterpret_cast<const NTFS_VOLUME_DATA_BUFFER *>(ioctl_buf);
   if (uuid && DeviceIoControl (volhdl, FSCTL_GET_NTFS_VOLUME_DATA, nullptr, 0,
-			       ioctl_buf, NT_MAX_PATH, &bytes_read, nullptr)
-      && nvdb->VolumeSerialNumber.QuadPart)
+			       ioctl_buf, NT_MAX_PATH, &bytes_read, nullptr))
     {
       /* Print without any separator as on Linux. */
-      __small_sprintf (name, "%16X", nvdb->VolumeSerialNumber.QuadPart);
+      __small_sprintf (name, "%016X", nvdb->VolumeSerialNumber.QuadPart);
       NtClose(volhdl);
       return true;
     }
@@ -327,13 +328,9 @@ partition_to_label_or_uuid(bool uuid, const UNICODE_STRING *drive_uname,
   FILE_FS_VOLUME_INFORMATION *ffvi =
     reinterpret_cast<FILE_FS_VOLUME_INFORMATION *>(ioctl_buf);
   if (uuid)
-    {
-      if (!ffvi->VolumeSerialNumber)
-	return false;
-      /* Print with separator as on Linux. */
-      __small_sprintf (name, "%04x-%04x", ffvi->VolumeSerialNumber >> 16,
-		       ffvi->VolumeSerialNumber & 0xffff);
-    }
+    /* Print with separator as on Linux. */
+    __small_sprintf (name, "%04x-%04x", ffvi->VolumeSerialNumber >> 16,
+		     ffvi->VolumeSerialNumber & 0xffff);
   else
     {
       /* Label is not null terminated. */
@@ -610,7 +607,7 @@ get_by_id_table (by_id_entry * &table, fhandler_dev_disk::dev_disk_location loc)
   if (!table)
     return (errno_set ? -1 : 0);
 
-  /* Sort by name and remove duplicates. */
+  /* Sort by name and mark duplicates. */
   qsort (table, table_size, sizeof (*table), by_id_compare_name);
   for (unsigned i = 0; i < table_size; i++)
     {
@@ -619,12 +616,13 @@ get_by_id_table (by_id_entry * &table, fhandler_dev_disk::dev_disk_location loc)
 	j++;
       if (j == i + 1)
 	continue;
-      /* Duplicate(s) found, remove all entries with this name. */
-      debug_printf ("removing duplicates %d-%d: '%s'", i, j - 1, table[i].name);
-      if (j < table_size)
-	memmove (table + i, table + j, (table_size - j) * sizeof (*table));
-      table_size -= j - i;
-      i--;
+      /* Duplicate(s) found, append "#N" to all entries.  This never
+	 introduces new duplicates because '#' never occurs in the
+	 original names. */
+      debug_printf ("mark duplicates %u-%u of '%s'", i, j - 1, table[i].name);
+      size_t len = strlen (table[i].name);
+      for (unsigned k = i; k < j; k++)
+	__small_sprintf (table[k].name + len, "#%u", k - i);
     }
 
   debug_printf ("table_size: %d", table_size);
-- 
2.42.1