Re: [PATCH v2 2/5] tap: Support for detection of existing sockets on ramfs

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Oct 31, 2022 at 12:20:56PM +0100, Stefano Brivio wrote:
> On ramfs, connecting to a non-existent UNIX domain socket yields
> EACCESS, instead of ENOENT. This is visible if we use passt directly
> on rootfs (a ramfs instance) from an initramfs image.
> 
> It's probably wrong for ramfs to return EACCES, but given the
> simplicity of the filesystem, I doubt we should try to fix it there
> at the possible cost of added complexity.

Yeah, that's deeply weird.  I'm not even sure how you'd get such a bug
involving the intersection of filesystem and unix socket.

> Also, this whole beauty should go away once qrap-less usage is
> established, so just accept EACCES as indication that a conflicting
> socket does not, in fact, exist.

That's reasonable, in addition, another case that would give EACCES is
if some other user has a passt instance running there, in which case
this is still probably the right thing to do.

> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  tap.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tap.c b/tap.c
> index 4dcff4f..0a3ccce 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -912,7 +912,8 @@ static void tap_sock_unix_init(struct ctx *c)
>  		}
>  
>  		ret = connect(ex, (const struct sockaddr *)&addr, sizeof(addr));
> -		if (!ret || (errno != ENOENT && errno != ECONNREFUSED)) {
> +		if (!ret || (errno != ENOENT && errno != ECONNREFUSED &&
> +			     errno != EACCES)) {
>  			if (*c->sock_path) {
>  				err("Socket path %s already in use", path);
>  				exit(EXIT_FAILURE);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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