bhyve: add helper to create a bootorder

[corvink]

Summary

Qemu's fwcfg allows to define a bootorder. Therefore, the hypervisor has
to create a fwcfg item named bootorder, which has a newline seperated
list of boot entries. Qemu's OVMF will pick up the bootorder and applies
it.

Add the moment, bhyve's OVMF doesn't support a custom bootorder by
qemu's fwcfg. However, in the future bhyve will gain support for qemu's
OVMF. Additonally, we can port relevant parts from qemu to bhyve's OVMF
implementation if desired.

[rew]

usr.sbin/bhyve/pci_emul.c

977

why negative error here?

1443–1444

1577

why not return the error instead?

[jhb]

usr.sbin/bhyve/pci_emul.c

975

Note that style(9) also really wants you to declare all the variables within a block up front.

982

A TAILQ is fine. If the logic is simpler, a growable array of pointers might be the other option to consider as then checking for a conflict is simpler I think. In the iteration case you just have to skip NULL pointers in the array.

1421

Have you considered using open_memstream() to construct this string? It will do all the realloc + NUL terminate for you letting you do something like:

struct boot_device *device;
FILE *fp;
char *bootorder;
size_t bootorder_len;

if (TAILQ_EMPTY(&boot_devices))
    return (0);

fp = open_memstream(&fp, &bootorder_len);
TAILQ_FOREACH(device, &boot_devices, boot_device_chain) {
    fwrite(fp, "/pci@i0cf8/pci@%d,%d\n", device->pdi->pdi_slot,
        device->pdi->pdi_func);
}
fclose(cp);

return (qemu_fwcfg_add_file("bootorder", bootorder_len, bootorder));

1573

The comment mostly duplicates the function name so you can probably omit it.

[corvink]

• fix style issues
• use memstream to build a bootorder fwcfg item

[jhb]

Just one more suggestion. If you decide to use fprintf, you can still count it as reviewed.

usr.sbin/bhyve/pci_emul.c

1426

Is the NAME_MAX restriction part of the fwcfg API for this node? If not, maybe just use fprintf directly without the bootpath temporary variable?

[markj]

usr.sbin/bhyve/pci_emul.c

989

1573