On Sat, Jul 01, 2006 at 01:08:17PM -0700, Linus Torvalds wrote:
> The argument that user space is more debuggable has been shown to be
> largely a red herring. User space is only more debuggable if it does
> something independent, and we've seen that user space is _harder_ to debug
> than kernel space if we have events going back and forth.
Agreed, 100%.
In addition, userspace is debuggable only only if the initramfs has
enough debugging code in their (like a real live working shell,
strace, basic shell commands etc.) Otherwise, it becomes even more
hellish to debug. I wasted a huge amount of time trying to figure out
why the RHEL4 initramfs was incompatible with modern kernels using the
MPT Fusion SCSI driver, because I couldn't make it stop and break out
to a working shell; it had some busybox-like nash thing that wasn't
designed for user interaction, so all I could do was try to make tiny
changes to the initramfs, wait for the !@#@# very long boot cycle, and
watch the initial ramdisk fail to mount the root and crash, and
repeat, for hours on end. RHEL4's userspace root mount system was
***not*** more debuggable, not in the last. Adding printk's into a
kernel and recompiling would have been easier, and far less
frustrating.
Hopefully kinit will be better, but it's definitely not the case that
userpsace is easier to debug.
- Ted
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