hurd: fix definition of utsname struct

[pinotree]

• drop the domainname field, as it is not actually used
• add a private _UTSNAME_LENGTH constant matching the helper libc one, to ease declaring the struct
• bump the size of the other fields to _UTSNAME_LENGTH

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[pinotree]

@sthibaul this should fix crashes when using this struct (by calling uname()); because of this, I'm nominating this for a backport in libc-0.2, even if "breaking".

@rustbot label stable-nominated

[pinotree]

For reference:

• sys/utsname.h: https://sourceware.org/git/?p=glibc.git;a=blob;f=posix/sys/utsname.h;h=c6884255e04595996dbbc337ac667d0defd035f3;hb=ab564362d0470d10947c24155ec048c4e14a009d
  • the general definition of the utsname struct
• bits/utsname.h: https://sourceware.org/git/?p=glibc.git;a=blob;f=bits/utsname.h;h=c5c57e840397d9efa6ad6a3b614569d094d26c21;hb=ab564362d0470d10947c24155ec048c4e14a009d
  • the actual bits used on Hurd, setting 1024 as fields size and not enabling domainname

[sthibaul]

agreed!

[tgross35]

Thanks for the sources, agreed that we can backport this (thanks for the ack @sthibaul).

Could you add const _UTSNAME_LENGTH: usize = 1024; and use that to make it a bit more consistent and greppable?

[pinotree]

Could you add const _UTSNAME_LENGTH: usize = 1024; and use that to make it a bit more consistent and greppable?

Makes sense, done so -- thanks for the suggestion!

[tgross35]

Thanks for the fix!