driver-core: devtmpfs - substitute (unreliable) device names with UUIDs

From: Kay Sievers <[email protected]>
Subject: driver-core: devtmpfs - substitute (unreliable) device names with UUIDs

For historic reasons, Linux uses very short abbreviated names for device nodes. Recent userspace development added various abstractions to access /dev, so that this is no longer necessary and we are able to switch almost all of them to proper UUIDs, which are better machine-readable, more extensible and future proof.

There is no need in the future to coordinate device names, or namespace them, the pool if IDs is just large enough to prevent any conflicts.

In this patch, for now, the 'memory' device nodes are excluded from that list, and /dev/null will still be created to support legacy systems, or to be able to boot directly with init=/bin/sh in a non-ported legacy shell binary.

This is the first part of a series of upcoming changes. We are working on and propose a similar scheme for the subsystem names in /sys, cgroups, network interfaces names. The other patches will be submitted when they have seen more testing, but all looks promising so far.

This is probably not appropriate for -stable, but we are currently working on making this feature configurable, so that it can be safely backported to older kernels.

This is an example output from a 3.4+ kernel:

  $ sh-4.2# ls -l /dev 
  total 0
    4,  17 Apr  1 14:47 0507f057-707a-4390-bcbc-28f7b8cea649
    4,  64 Apr  1 14:47 075d204b-1eaf-4fa9-9e31-f08a3dd6783d
   10, 228 Apr  1 14:47 07c45fc1-d32c-4bde-99f2-ebf746ab0d70
    4,  45 Apr  1 14:47 0ddd2345-c18f-4ea4-a85d-eff1be877d9a
    4,  66 Apr  1 14:47 135ba1fb-019e-409b-922a-38ede939384f
    4,  38 Apr  1 14:47 176eee40-89ce-45b8-bf36-0caee0aded21
    7,   0 Apr  1 14:47 18074259-9dad-4700-9ad0-48bee2cdd677
    4,   8 Apr  1 14:47 1989db1b-317e-44a2-bf31-f874c9091b12
    4,  49 Apr  1 14:47 1be81e3a-02ee-437b-9163-3b448b8909a0
  254,   0 Apr  1 14:47 1c68dffe-a80a-44f4-a956-2d4a2d1bd897
    7, 128 Apr  1 14:47 1d78abd2-3f49-43b0-8497-715ed06dfc0a
    4,  23 Apr  1 14:47 1ebce641-d889-4088-b14e-c5edbc52ecfc
    4,  50 Apr  1 14:47 21df754f-a826-4162-b687-8c4a35f68b91
    4,  34 Apr  1 14:47 22378a55-7c3f-4ea2-a8a7-c01e1c5ab756
    4,  39 Apr  1 14:47 2254905d-b071-427c-8566-cfd4b1a31524
    5,   0 Apr  1 14:47 22dae2a8-862a-4a4e-ab46-25a7c0177f9e
    4,  59 Apr  1 14:47 2491d450-fad2-40bc-9563-4d65c3c68ce0
    4,  67 Apr  1 14:47 2a975f05-f3b4-48e4-af2b-b2b0712de780
    4,  55 Apr  1 14:47 2ae0c894-0a67-4610-a05d-ff2aae1d0d64
  253,   0 Apr  1 14:47 2d0058bb-38b9-438d-8aaa-b7d9e02991f8
    4,  61 Apr  1 14:47 2d4c584e-8f19-48b4-9f50-67a46839b950
    5,   1 Apr  1 14:47 2e6ab566-7919-4d5a-b0e6-664a5d066b30
   10,  62 Apr  1 14:47 2e85a7c8-bd1d-4263-b79d-947423368beb
    4,  58 Apr  1 14:47 3000ffd8-3d35-4350-bfbc-225ac991f653
    4,   0 Apr  1 14:47 33959aa5-3834-4944-82eb-1560a5226d94
    4,   7 Apr  1 14:47 33b969a4-5cc5-40ea-9494-5316a65f8cd6
   10, 227 Apr  1 14:47 34aff009-3a8b-4a01-827e-f5a9975c2058
    4,  20 Apr  1 14:47 3f2491aa-bcb1-4948-a20f-15f6a07bf70c
    4,   5 Apr  1 14:47 42c194bb-82b9-4823-966e-1328d75ab3e6
    4,  44 Apr  1 14:47 43f0ade0-4588-4944-9ec5-089c9ae359e0
    4,  29 Apr  1 14:47 44d0411d-8ff1-4fe2-bf6e-44679e08c03c
    4,  37 Apr  1 14:47 46cbdd3b-bd2e-446f-94a2-837811e4a7f8
    4,   6 Apr  1 14:47 473a613d-1ae5-47e2-8c55-6f76bb83be53
    4,  46 Apr  1 14:47 4802c9ef-0162-40e6-996f-59ded6badd2a
    4,  21 Apr  1 14:47 4a402517-0bef-4814-8671-4ea5c13279d1
    4,  47 Apr  1 14:47 4cc6b5b0-2baa-43df-a2f1-0d38ddb17ed1
    4,   3 Apr  1 14:47 4e87cf2a-448d-4dad-a4c9-00a14d5a6c8b
    4,   1 Apr  1 14:47 5409fb4c-62b9-4467-9be2-0063bb7ed7fe
    4,  16 Apr  1 14:47 554e8e04-0e27-4420-bcf6-5d8acc897706
    4,  30 Apr  1 14:47 55a1fef8-e286-401e-9b00-62ae190985a8
    4,  13 Apr  1 14:47 577b1fd0-9606-4b46-8e15-a84a5758b6be
    4,  56 Apr  1 14:47 5867cffc-636a-4625-beb7-1077f7e1c4a4
    4,  57 Apr  1 14:47 5c8de8e8-824b-49c7-ba28-2fba017285b7
    4,  28 Apr  1 14:47 5e4b3c75-62e7-417e-8f54-fc2ce49a418f
    4,  54 Apr  1 14:47 624f2852-0bde-497a-88a6-c4a6d8fd739c
    4,  41 Apr  1 14:47 645a47a6-902d-4870-95df-26170348285b
    4,  48 Apr  1 14:47 66666ae9-bfaf-478f-9773-3fbb275dfd8b
    4,  60 Apr  1 14:47 67b7f875-c80a-4b40-b619-0af37041d1ab
    4,  32 Apr  1 14:47 69278743-4cfa-48d3-ae82-7534c61a60b7
    4,  24 Apr  1 14:47 6a82c453-a38d-490f-82ce-4d021ae123cd
    4,  15 Apr  1 14:47 6ac64fb5-c52c-451e-8146-8a796b7351bd
    4,  33 Apr  1 14:47 71614a99-cc50-4fd5-8a8a-ece7009de1ab
    4,  19 Apr  1 14:47 7682c236-2b58-4beb-b1e1-5a00f3a1cc46
    4,  10 Apr  1 14:47 76b2adf3-ddd6-46e6-9024-831cad4786a7
    4,  51 Apr  1 14:47 774e198a-96a8-434b-957a-d20cd3590f01
   10,   1 Apr  1 14:47 7b503243-9b10-4d83-bb07-a057a7d4abac
    7, 129 Apr  1 14:47 7d0bee34-abbd-4f1c-80a9-3eed29ad11e9
    4,  42 Apr  1 14:47 7d627d64-520d-4cd9-ac3d-42d22a876aed
    4,   2 Apr  1 14:47 834d656e-488a-4c0a-894c-aba4bff74b9c
    4,  18 Apr  1 14:47 85d5061c-dd48-4804-a6cb-a22d26d91a5e
    4,   4 Apr  1 14:47 882f3674-2b74-42f7-b64b-80b4e01b3dd0
    4,  64 Apr  1 14:47 8e693fd0-a50e-465d-9c0b-a74e41943dbb
    4,  35 Apr  1 14:47 8ec6b3e6-8d72-4ad9-aba9-8a91ef3f2c3b
    4,  31 Apr  1 14:47 9a29e09a-7cae-4d68-8ba0-99d103a12900
    4,  63 Apr  1 14:47 9ccf9199-ae2c-4843-a764-36ed02e88dba
    5,   2 Apr  1 14:47 a07ff4c4-ac59-4496-ad43-d6f95414fc7b
   13,  63 Apr  1 14:47 a93508ca-af17-495a-b0d0-09870e1897b7
   10,  61 Apr  1 14:47 ace2077a-e328-42b5-b403-63d97978832f
    4,  40 Apr  1 14:47 afadf815-4671-4602-8b90-86b5be540d2b
    4,  62 Apr  1 14:47 b24c5416-25f2-4349-88c6-7ebb610910b1
    8,   3 Apr  1 14:47 b2e91dad-3137-4294-b6d1-8a9b3e868883
    7,   1 Apr  1 14:47 b7087629-68a1-4c8f-8548-395c50a3e810
    4,  11 Apr  1 14:47 b7c70fed-aea9-47b9-b480-fd5905c960f0
    4,  52 Apr  1 14:47 b96d8283-538d-4d1e-afa1-10341a3ab4b5
    4,   9 Apr  1 14:47 bc32ed02-00d5-4ccf-b8b5-e4eb382a5b68
   10, 235 Apr  1 14:47 bc4e4e01-1754-41dc-9482-345076660cbd
    8,   4 Apr  1 14:47 be68b2f4-568e-466c-a287-a7d89670b5ea
   10, 234 Apr  1 14:47 c3105ce0-1fa9-47ec-a0e6-bf8cf72d380b
    4,  12 Apr  1 14:47 c5279776-5d30-417f-8e58-fd142960638a
    4,  65 Apr  1 14:47 c7f1cf12-2da8-49c9-886b-ad99d9c5cd41
    8,   2 Apr  1 14:47 c9b0b801-2117-42cf-9720-4d10678c6227
    8,   0 Apr  1 14:47 ce9c6e97-be60-4637-9c00-23abb2d40dfa
    8,   1 Apr  1 14:47 d0098815-5fee-4818-85c0-06002273319e
    4,  26 Apr  1 14:47 d3edd26e-6a39-49b7-8653-ad7a322c5ffc
  253,   1 Apr  1 14:47 d56b4e1e-9331-4a20-8b56-2be2ee0508f6
    4,  22 Apr  1 14:47 df4023ec-ce6a-408c-a96a-3dec9883e625
    4,  27 Apr  1 14:47 e0d51a34-4a4a-4da7-b580-38cf5432744f
    4,  53 Apr  1 14:47 e26ad6e6-d8e2-48be-8d2c-2f0b16abff08
   13,  32 Apr  1 14:47 ec8358f2-3e38-4e06-bd2c-68bde8ec7d1b
    4,  36 Apr  1 14:47 ef941460-6397-4126-bd23-d55ee8b520aa
    4,  14 Apr  1 14:47 f1341ce0-9475-4113-aff3-5cbf926a41ef
    4,  25 Apr  1 14:47 f4663273-d255-4151-bde9-feb7593a427e
    4,  43 Apr  1 14:47 f52e3619-5765-4942-9d70-3553195cec99
   10,  63 Apr  1 14:47 fe0dde7a-4047-41c1-ae55-548d20dad81a
    1,   7 Apr  1 14:47 full
    1,   2 Apr  1 14:47 kmem
    1,  11 Apr  1 14:47 kmsg
    1,   1 Apr  1 14:47 mem
    1,   3 Apr  1 14:47 null
    1,   4 Apr  1 14:47 port
    1,   8 Apr  1 14:47 random
    1,   9 Apr  1 14:47 urandom
    1,   5 Apr  1 14:47 zero

---
 core.c |   42 ++++++++++++++++++++++++++++++++++++++++++++---------------------
 1 file changed, 16 insertions(+), 26 deletions(-)

index e28ce98..8433f16 100644
@@ -25,6 +25,7 @@
 #include <linux/mutex.h>
 #include <linux/async.h>
 #include <linux/pm_runtime.h>
+#include <linux/netdevice.h>
 
 #include "base.h"
 #include "power/power.h"

@@ -1259,32 +1260,19 @@ static struct device *next_device(struct klist_iter *i)
 const char *device_get_devnode(struct device *dev,
                               umode_t *mode, const char **tmp)
 {
-       char *s;
+       unsigned char bytes[16];
 
-       *tmp = NULL;
-
-       /* the device type may provide a specific name */
-       if (dev->type && dev->type->devnode)
-               *tmp = dev->type->devnode(dev, mode);
-       if (*tmp)
-               return *tmp;
-
-       /* the class may provide a specific name */
-       if (dev->class && dev->class->devnode)
-               *tmp = dev->class->devnode(dev, mode);
-       if (*tmp)
-               return *tmp;
-
-       /* return name without allocation, tmp == NULL */
-       if (strchr(dev_name(dev), '!') == NULL)
-               return dev_name(dev);
-
-       /* replace '!' in the name with '/' */
-       *tmp = kstrdup(dev_name(dev), GFP_KERNEL);
+       *tmp = kmalloc(36, GFP_KERNEL);
        if (!*tmp)
                return NULL;
-       while ((s = strchr(*tmp, '!')))
-               s[0] = '/';
+
+       if (dev->class && !strcmp("mem", dev->class->name)) {
+               *tmp = kstrdup(dev_name(dev), GFP_KERNEL);
+       } else {
+               generate_random_uuid(bytes);
+               sprintf(*tmp, "%pU", bytes);
+       }
+
        return *tmp;
 }
 

Nice job, now applied, thanks.

greg k-h