[PATCH] tdb: introduce tdb_chainlock_read_nonblock()

[Alexander Drozdov]

I've just found that exactly the same function & implementation was suggested
by Kirill Smelkov 5 years ago, but it was rejected:

https://lists.samba.org/archive/samba-technical/2010-October/073695.html

On 24.04.2015 08:09:02 +0300 Alexander Drozdov <al.drozdov at gmail.com> wrote:
> tdb has nonblock variants for many lock functions, for example:
>
> tdb_lockall() / tdb_lockall_nonblock()
> tdb_lockall_read() / tdb_lockall_read_nonblock()
> tdb_chainlock() / tdb_chainlock_nonblock()
>
> But there hasn't been nonblock variant for tdb_chainlock_read().