improving support issues with "tail -f / unrecognized file systems"

[Assaf Gordon]

Hi all,

I was thinking how to improve the situation where users complain about
"unrecognized file systems" errors in "tail -f".
(as in the recent 
https://lists.gnu.org/archive/html/coreutils/2017-11/msg00043.html ).

This is not their "fault", as they simply have an older version
installed, and it is not our "fault", as the file system is likely
already supported in newer versions.

It is simply a matter of making it easier for users to understand what's
going on, and easier for us to not have to answer the same thing again 
and again.

I suggest the following:

1. a script that can detect which file systems are supported -
there's already one working in 'src/extract-magic'.

2. improve the script to also detect which in which version
the file system is supported (POC attached).

3. Generate an HTML page listing each filesystem, the magic value,
 and the minimal version it is supported in.
something like:

  Hello,
  If you are seeing the error message:

     unrecognized file system type [[0x794c7630]]

  This error is reported when reading files on [[OVERLAYFS]] file
  system. Support for [OVERLAYFS] was added in Coreutils version
  [v8.28].
  Upgrade coreutils version to avoid this warning.
  To see which version  you are using, run "tail --version".

  This warning is harmless - 'tail' will still operate correctly
  on your filesystem, although not as efficient as possible.

  If you have any further questions, please contact address@hidden


5. We modify 'tail' to point the user to the web page instead
of reporting a bug.

6. when new filesystems are added, just update the webpage.

What do you think ?

Attached is a proof-of-concept script implementing step 2.
Usage like so:

$ perl prepare-fs-support src/stat.c | head
 magic-value  c-constant              availble-in-version  human-name
      0xADF5  S_MAGIC_ADFS            v8.15                adfs
      0xADFF  S_MAGIC_AFFS            v8.15                affs
  0x5346414F  S_MAGIC_AFS             v8.15                afs
  0x09041934  S_MAGIC_ANON_INODE_FS   v8.15                anon-inode FS
      0x0187  S_MAGIC_AUTOFS          v8.15                autofs
  0x42465331  S_MAGIC_BEFS            v8.15                befs
  0x1BADFACE  S_MAGIC_BFS             v8.15                bfs
  0x9123683E  S_MAGIC_BTRFS           v8.15                btrfs
  0x0027E0EB  S_MAGIC_CGROUP          v8.15                cgroupfs

Of course, it doesn't even have to be an automated process with a perl 
script, we can just update a web page manually when a new filesystem is 
added.


Comments welcomed,
   -assaf

prepare-fs-support
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