Remove redundant errno save

In D54641#1263851, @markj wrote:

I guess this mostly relates to support for legacy and 32-bit guest operating systems? I tend to think it's undesirable to break support for them, given that virtualizing legacy systems is a major reason to use bhyve in the first place, at least in principle.

Does it simplify things at all to use a single vmem arena for both 32-bit and 64-bit memory BARs, and apply constraints as needed when calling vmem_xalloc()?

Fix PCI passthrough:

• Introduce a state machine that tracks a BAR's address. This allows us to properly release and allocate BAR addresses from the appropriate pool when the guest starts migrating BARs
• Comply with the remark in pci_emul_assign_bar and allocate small MEM64 BARs from the MEM32 pool
• Allow the guest to move an already allocated BAR to a new address

In D54641#1258945, @markj wrote:

Have you tested with PCI passthru configured? With just this patch applied, I get an assertion failure in update_bar_address(). Same result if I test your github branch.

LGTM.

Address @markj 's comment - switch to INTERNALLIB

Address @markj 's comments.

Address @markj 's comments.

In D54641#1258945, @markj wrote:

Have you tested with PCI passthru configured? With just this patch applied, I get an assertion failure in update_bar_address(). Same result if I test your github branch.

Address @markj 's comments.

Address @markj 's comments.

Use procdesc(4) to enable slirp backend hotplugging.

Fix slirp_init_fds.

Fix the LIBBHYVEDIR variable.

Account for latest changes in D54650.

• constify command nvlist_t argument
• adapt vm_do_checkpoint to use the new return type

Account for latest changes in D54650.

Address @rew 's comments - change IPC command return type to nvlist_t.

Address @rew 's comments.

Address @rew 's comments.

Address @markj 's comments.