Re: Working with user space file descriptor in kernel thread

[email protected] (Mouse) writes:

>> My question is:
>> Can I use such retrieved file_fd or struct socket* so in separate
>> kernel thread ?

>I see no reason why not - but that is not at all the same as "yes".  I
>do not work with multiple threads often enough to feel confident of my
>answer here.


The kernel iSCSI initiator takes a file descriptor from
userland and then uses the socket in two separate threads,
one sending, one receiving.

While the two threads use a rwlock to protect the socket,
they acquire it in shared ("READER") mode for I/O and
in exclusive ("WRITER") mode for closing and replacing
during error recovery.

The socket operations themselves are protected by the
socket lock. In case of PF_INET that's a global lock
(even with NET_MPSAFE). In case of PF_LOCAL, each
socket has a private lock.