Re: Reminder: NET_NEEDS_GIANT, debug.mpsafenet going away in 7.0


On Tue, 17 Jul 2007, Pascal Hofstee wrote:

On Tue, 2007-07-17 at 13:21 +0100, Robert Watson wrote:

This is a reminder e-mail that, in the very near future, Giant compatibility shims for network protocols will be removed. These shimmed allowed Giant to be re-enabeld over the network stack as a result of linking in a service that required Giant (now all removed), or by setting the debug.mpsafenet variable to 1. This means that the following will no longer be present:

debug.mpsafenet sysctl
debug_mpsafenet global variable
NET_NEEDS_GIANT()
NET_LOCK_GIANT(), NET_UNLOCK_GIANT(), NET_ASSERT_GIANT()
NET_CALLOUT_MPSAFE

All instances of NET_{LOCK,UNLOCK,ASSERT}_GIANT() will be removed as they will no be no-ops.

Ehrm ... i am not 100% sure here but what will this mean for those of us running qemu on 7.x systems ... if i recall correctly qemu requires aio for at least DMA which on 6.x at least still issues below warning when kldloaded:

WARNING: Network stack Giant-free, but aio requires Giant.
Consider adding 'options NET_WITH_GIANT' or setting
debug.mpsafenet=0

Does this removal of debug.mpsafenet mean that aio on CURRENT is now GIANT free .. or does this mean that we'll be seeing problems with qemu on CURRENT ?

I believe that davidxu did the work in 7.0 to make aio MPSAFE -- you should not get the above warning with 7.x, only 6.x. The warning is generated by NET_NEEDS_GIANT("aio") in vfs_aio.c, and as of last week, there are no NET_NEEDS_GIANT() callers in 7.x (hence removing the infrastructure for it).

Robert N M Watson
Computer Laboratory
University of Cambridge
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