As with struct ethhdr, the musl libc provides its own definition of the iphdr struct. This guard ensures software like net-tools builds correctly on the musl libc. The __UAPI_DEF_IPHDR definition is in ip.h itself to prevent the issue in commit da360299b673 ("uapi/if_ether.h: move __UAPI_DEF_ETHHDR libc define") from being seen here. Signed-off-by: A. Wilcox <AWilcox@Wilcox-Tech.com> --- include/uapi/linux/ip.h | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/include/uapi/linux/ip.h b/include/uapi/linux/ip.h index e42d13b55cf3..d34a0d295672 100644 --- a/include/uapi/linux/ip.h +++ b/include/uapi/linux/ip.h @@ -83,6 +83,13 @@ #define IPV4_BEET_PHMAXLEN 8 +/* Allow libcs to deactivate this - musl has its own copy in <netinet/ip.h> */ + +#ifndef __UAPI_DEF_IPHDR +#define __UAPI_DEF_IPHDR 1 +#endif + +#if __UAPI_DEF_IPHDR struct iphdr { #if defined(__LITTLE_ENDIAN_BITFIELD) __u8 ihl:4, @@ -104,6 +111,7 @@ struct iphdr { __be32 daddr; /*The options start here. */ }; +#endif struct ip_auth_hdr { -- 2.22.1
From: "A. Wilcox" <AWilcox@Wilcox-Tech.com>
Date: Sun, 22 Dec 2019 00:02:27 -0600
> @@ -83,6 +83,13 @@
>
> #define IPV4_BEET_PHMAXLEN 8
>
> +/* Allow libcs to deactivate this - musl has its own copy in <netinet/ip.h> */
> +
> +#ifndef __UAPI_DEF_IPHDR
> +#define __UAPI_DEF_IPHDR 1
> +#endif
How is this a musl-only problem? I see that glibc also defines struct iphdr
in netinet/ip.h, so why doesn't it also suffer from this?
I find it really strange that this, therefore, only happens for musl
and we haven't had thousands of reports of this conflict with glibc
over the years.
I want an explanation, and suitably appropriate adjustments to the commit
message and comments of this change.
Thank you.
On Wed, Dec 25, 2019 at 04:34:11PM -0800, David Miller wrote: > From: "A. Wilcox" <AWilcox@Wilcox-Tech.com> > Date: Sun, 22 Dec 2019 00:02:27 -0600 > > > @@ -83,6 +83,13 @@ > > > > #define IPV4_BEET_PHMAXLEN 8 > > > > +/* Allow libcs to deactivate this - musl has its own copy in <netinet/ip.h> */ > > + > > +#ifndef __UAPI_DEF_IPHDR > > +#define __UAPI_DEF_IPHDR 1 > > +#endif > > How is this a musl-only problem? I don't think it is, unless glibc's includes linux/ip.h to get the definition, which does not seem to be the case -- at least not on the Debian system I had handy to check on. > I see that glibc also defines struct iphdr > in netinet/ip.h, so why doesn't it also suffer from this? Maybe it does. > I find it really strange that this, therefore, only happens for musl > and we haven't had thousands of reports of this conflict with glibc > over the years. It's possible that there's software that's including just one of the headers conditional on __GLIBC__, and including both otherwise, or something like that. Arguably this should be considered unsupported usage; there are plenty of headers where that doesn't work and shouldn't be expected to. > I want an explanation, and suitably appropriate adjustments to the commit > message and comments of this change. Agreed. Commit messages should not imply that something is a musl-specific workaround when it's generally the right thing to do. Rich
From: Rich Felker <dalias@libc.org>
Date: Wed, 25 Dec 2019 20:05:15 -0500
> On Wed, Dec 25, 2019 at 04:34:11PM -0800, David Miller wrote:
>> I find it really strange that this, therefore, only happens for musl
>> and we haven't had thousands of reports of this conflict with glibc
>> over the years.
>
> It's possible that there's software that's including just one of the
> headers conditional on __GLIBC__, and including both otherwise, or
> something like that. Arguably this should be considered unsupported
> usage; there are plenty of headers where that doesn't work and
> shouldn't be expected to.
I don't buy that, this is waaaaaay too common a header to use.
Please investigate.
On Thu, Dec 26, 2019, at 04:49, David Miller wrote: > From: Rich Felker <dalias@libc.org> > Date: Wed, 25 Dec 2019 20:05:15 -0500 > > > On Wed, Dec 25, 2019 at 04:34:11PM -0800, David Miller wrote: > >> I find it really strange that this, therefore, only happens for musl > >> and we haven't had thousands of reports of this conflict with glibc > >> over the years. > > > > It's possible that there's software that's including just one of the > > headers conditional on __GLIBC__, and including both otherwise, or > > something like that. Arguably this should be considered unsupported > > usage; there are plenty of headers where that doesn't work and > > shouldn't be expected to. > > I don't buy that, this is waaaaaay too common a header to use. In case of net-tools, only <linux/ip.h> is included, and never <netinet/ip.h> directly. Chances are in musl the indirect include tree happens to be different and conflicting, while in glibc it is not. > > Please investigate. > Daniel
On Thu, Dec 26, 2019 at 12:13:37PM +0100, Daniel Kolesa wrote:
> On Thu, Dec 26, 2019, at 04:49, David Miller wrote:
> > From: Rich Felker <dalias@libc.org>
> > Date: Wed, 25 Dec 2019 20:05:15 -0500
> >
> > > On Wed, Dec 25, 2019 at 04:34:11PM -0800, David Miller wrote:
> > >> I find it really strange that this, therefore, only happens for musl
> > >> and we haven't had thousands of reports of this conflict with glibc
> > >> over the years.
> > >
> > > It's possible that there's software that's including just one of the
> > > headers conditional on __GLIBC__, and including both otherwise, or
> > > something like that. Arguably this should be considered unsupported
> > > usage; there are plenty of headers where that doesn't work and
> > > shouldn't be expected to.
> >
> > I don't buy that, this is waaaaaay too common a header to use.
>
> In case of net-tools, only <linux/ip.h> is included, and never
> <netinet/ip.h> directly. Chances are in musl the indirect include
> tree happens to be different and conflicting, while in glibc it is
> not.
musl has no indirect inclusion of netinet/ip.h from standard headers,
but does include it from netinet/ip_icmp.h. It seems glibc only does
this conditional on __USE_MISC, which doesn't make much sense to me
since this is not a standardized header with namespace rules, but
normally __USE_MISC is defined anyway on glibc so I kinda doubt this
is the difference.
Any other ideas?
Rich