bug#10349: tail: fix --follow on FhGFS remote file systems

[Jim Meyering]

Pádraig Brady wrote:
> On 12/22/2011 11:48 PM, Pádraig Brady wrote:
>> On 12/22/2011 09:50 PM, Alan Curry wrote:
>>> Bob Proulx writes:
>>>>
>>>> Jim Meyering wrote:
>>>>> Are there so many new remote file systems coming into use now?
>>>>> That are not listed in /usr/include/linux/magic.h?
>>>>
>>>> The past can always be enumerated.  The future is always changing.  It
>>>> isn't possible to have a complete list of future items.  It is only
>>>> possible to have a complete list of past items.  The future is not yet
>>>> written.
>>>
>>> Between past and future is the present, i.e. the currently running kernel.
>>> Shouldn't it return an error when you use an interface that isn't 
>>> implemented
>>> by the underlying filesystem? Why doesn't this happen?
>>
>> That's a fair point.
>>
>> Eric shouldn't some/all remote file systems in the kernel
>> return ENOTSUP for inotify operations?
>
> Oh right, as Sven points out,
> a notification _is_ sent for local processes modifying a remote file.
> I guess we'd need a IN_REMOTE flag (send remote events too), which
> remote file systems would return ENOTSUP if they don't support that.
> That's getting a bit awkward though.

I'm thinking of recording[*] which file systems are local and which
are remote.  Then we can make tail -f warn when one or more of
its file arguments resides on a remote file system.  We may finally
have to add and document --disable-inotify.

Jim

[*] It's easy to record local/remote in a table from which a switch stmt
or gperf table is derived, just as is currently done for FS magic numbers.