Re: compat: autofs v5 packet size ambiguity - update

[H. Peter Anvin]

On 02/21/2012 09:43 PM, Ian Kent wrote:
> 
> However, with the final "char name[NAME_MAX+1]" array at the end, the
> actual size of the structure ends up being not very well defined:
> because the struct isn't marked 'packed', doing a "sizeof()" on it will
> align the size of the struct up to the biggest alignment of the members
> it has.
> 

Note that it's really rather unfortunate that this transmits the entire
packet no matter what, which also means that the "len" field is actually
completely and totally pointless.

I have mentioned in the past that I consider it a design mistake on my
part to have used a pipe in the first place: it was "so easy", but
required an extra read for no good reason, or padding to fixed size
resulting in this problem.  The right thing really should have been to
use a Unix datagram socket; these days using SOCK_SEQPACKET - that way
the kernel would give you the right semantics by design.

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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