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 17:45, Christian Franke wrote:
>> Corinna Vinschen wrote:
>>> On Nov 17 15:39, Christian Franke wrote:
>>>> The last two /dev/disk subdirectories :-)
>>>>
>>>> Note a minor difference: On Linux, empty /dev/disk subdirectories apparently
>>>> never appear. A subdirectory is not listed in /dev/disk if it would be
>>>> empty. Not worth the effort to emulate.
>>> Agreed.  This is really great.  I just pushed your patch.
>>>
>>> However, there's something strange in terms of by-label:
>>>
>>> I have two partitions with labels:
>>>
>>>     $ ls -l /dev/disk/by-label
>>>     total 0
>>>     lrwxrwxrwx 1 corinna vinschen 0 Nov 17 17:18 blub -> ../../sda3
>>>     lrwxrwxrwx 1 corinna vinschen 0 Nov 17 17:18 blub2 -> ../../sdb2
>>>     $
>>>
>>> Now I change the label of sdb2 to the same "blub" string as on sda3:
>>>
>>>     $ ls -l /dev/disk/by-label
>>>     total 0
>>>     $
>>>
>>> I'd expected to see only one, due to the name collision, but en empty
>>> dir is a bit surprising...  And it may occur more often than not, given
>>> that the default label "New_Volume" probably won't get changed very
>>> often.
>>>
>> This is intentional and inherited from the very first patch, see the loop
>> behind qsort(). If a range of identical names appear, all these entries are
>> removed. If some "random" entry would be kept, it might no longer be the
>> persistent link the user expects. We could possibly add some hash like done
>> for by-id or append a number in such cases later. Need some more time to
>> thing about it....
> 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 :-)
IIRC in the past I've seen in another of these directories (by-id?) that 
'#N' was appended if duplicates occur.


>> I will sent a patch for the new-features doc soon.

Attached.

Christian


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From 5d1c82f08e4b37d65acc8bf0c76f75641d762667 Mon Sep 17 00:00:00 2001
From: Christian Franke <christian.franke@t-online.de>
Date: Fri, 17 Nov 2023 18:41:08 +0100
Subject: [PATCH] Cygwin: Document /dev/disk/by-* subdirectories

Signed-off-by: Christian Franke <christian.franke@t-online.de>
---
 winsup/cygwin/release/3.5.0 | 16 +++++++++++-----
 winsup/doc/new-features.xml | 20 +++++++++++---------
 2 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/winsup/cygwin/release/3.5.0 b/winsup/cygwin/release/3.5.0
index 2d59818b5..aee21c972 100644
--- a/winsup/cygwin/release/3.5.0
+++ b/winsup/cygwin/release/3.5.0
@@ -17,11 +17,17 @@ What's new:
   class expressions, and collating symbols in the search pattern, i.e.,
   [:alnum:], [=a=], [.aa.].
 
-- Introduce /dev/disk directory with subdirectories by-id and by-partuuid.
-  The by-id directory provides symlinks for each disk and its partitions:
-  BUSTYPE-[VENDOR_]PRODUCT_[SERIAL|HASH][-partN] -> ../../sdX[N].
-  The by-partuuid directory provides symlinks for each MBR and GPT disk
-  partition: MBR_SERIAL-OFFSET -> ../../sdXN, GPT_GUID -> ../../sdXN.
+- Introduce /dev/disk directory with various by-* subdirectories which
+  provide symlinks to disk and partition raw devices:
+  by-drive/DRIVE_LETTER ->  ../../sdXN
+  by-label/VOLUME_LABEL ->  ../../sdXN
+  by-id/BUSTYPE-[VENDOR_]PRODUCT_[SERIAL|0xHASH][-partN] -> ../../sdX[N]
+  by-partuuid/MBR_SERIAL-OFFSET -> ../../sdXN
+  by-partuuid/GPT_GUID -> ../../sdXN
+  by-uuid/VOLUME_SERIAL -> ../../sdXN
+  by-voluuid/MBR_SERIAL-OFFSET -> ../../sdXN
+  by-voluuid/VOLUME_GUID -> ../../sdXN
+  The subdirectories by-drive and by-voluuid are Cygwin specific.
 
 - Introduce /proc/codesets and /proc/locales with information on
   supported codesets and locales for all interested parties.  Locale(1)
diff --git a/winsup/doc/new-features.xml b/winsup/doc/new-features.xml
index a8e8a7991..2c31a4acc 100644
--- a/winsup/doc/new-features.xml
+++ b/winsup/doc/new-features.xml
@@ -35,17 +35,19 @@ class expressions, and collating symbols in the search pattern, i.e.,
 </para></listitem>
 
 <listitem><para>
-Introduce /dev/disk directory with subdirectories by-id and by-partuuid.
-The by-id directory provides symlinks for each disk and its partitions:
+Introduce /dev/disk directory with various by-* subdirectories which
+provide symlinks to disk and partition raw devices:
   <screen>
-  BUSTYPE-[VENDOR_]PRODUCT_[SERIAL|0xHASH][-partN] -> ../../sdX[N]
-  </screen>
-The by-partuuid directory provides symlinks for each MBR and GPT disk
-partition:
-  <screen>
-  MBR_SERIAL-OFFSET -> ../../sdXN
-  GPT_GUID -> ../../sdXN
+  by-drive/DRIVE_LETTER ->  ../../sdXN
+  by-label/VOLUME_LABEL ->  ../../sdXN
+  by-id/BUSTYPE-[VENDOR_]PRODUCT_[SERIAL|0xHASH][-partN] -> ../../sdX[N]
+  by-partuuid/MBR_SERIAL-OFFSET -> ../../sdXN
+  by-partuuid/GPT_GUID -> ../../sdXN
+  by-uuid/VOLUME_SERIAL -> ../../sdXN
+  by-voluuid/MBR_SERIAL-OFFSET -> ../../sdXN
+  by-voluuid/VOLUME_GUID -> ../../sdXN
   </screen>
+The subdirectories by-drive and by-voluuid are Cygwin specific.
 </para></listitem>
 
 <listitem><para>
-- 
2.42.1