Re: [Xen-devel] [PATCH][TOOLS] libfsimage: portability fixes

[Christoph Egger <Christoph.Egger@xxxxxxx>]

On Thursday 27 March 2008 11:54:41 Ian Jackson wrote:
> Christoph Egger writes ("[Xen-devel] [PATCH][TOOLS] libfsimage: portability 
fixes"):
> > -SUBDIRS-y += $(shell env CC="$(CC)" ./check-libext2fs)
> > +SUBDIRS-y += $(shell $(SHELL) env CC="$(CC)" ./check-libext2fs)
>
> What purpose does this serve ?

Everytime when I submitted a patch where I changed /bin/bash to /bin/sh
John Levon came up with a "Build is broken on Solaris" message.
The fix was always the same: Use $(SHELL) as this is explicitely set for
Solaris.

> > +   /*
> > +    * Make reads from a raw disk sector-aligned. This is a requirement
> > +    * for NetBSD. Split the read up into to three parts to meet this
> > +    * requirement.
> > +    */
>
> Please forgive my ignorance: Does NetBSD offer a different (non-raw)
> device which does not have this requirement.  If so perhaps we should
> be using it instead - if not, why not ?

The raw device pass requests directly to the underlying device, with
only check/adjustments against the partition bounds. Especially it won't
try to do read/modify/write for write requests, or expand the read if it's
not sector-aligned.

The block device doesn't have this restriction, but allows only ONE open,
therefore it is not usable by pygrub. It also has other side-effects
(as it goes through the buffer cache), it's definitively not useable for the 
NetBSD block device *backend*   or for qemu-dm I/O.

Christoph


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