Enable user mode network backend support in qemu

[wangpc-pp]

If libslirp is found during configuration, it will be enabled.
So we just need install libslirp before building.

[cmuellner]

Are you sure that this is needed?
Afaik that's automatically discovered and enabled if the library is available.
So, I believe the only thing needed is to install libslirp-dev or libslirp-devel.

[TommyMurphyTM1234]

Are you sure that this is needed? Afaik that's automatically discovered and enabled if the library is available. So, I believe the only thing needed is to install libslirp-dev or libslirp-devel.

And only specifically when -netdev user is employed - which may not be the common case?

• https://wiki.qemu.org/ChangeLog/7.2

I agree with @cmuellner that such dependencies should be installed rather than built - unless there is a compelling case for building them from scratch as part of the riscv-gnu-toolchain build process.

Perhaps the potential dependency should be mentioned in the readme? But it's difficult to keep up with all possible dependencies for all situations on all platforms as evidenced by a few open issues:

• README.md prerequisites section is incomplete #1251
• Missing build instructions for MacOS running MacPorts in README.md #1332
• etc...

[wangpc-pp]

Are you sure that this is needed? Afaik that's automatically discovered and enabled if the library is available. So, I believe the only thing needed is to install libslirp-dev or libslirp-devel.

I think it's not enough, it complains:

network backend 'user' is not compiled into this binary

And as the doc says, we still need to enable it explicitly:

... this might be caused by the missing "user" mode backend. In that case, please install libslirp first ("dnf install libslirp-devel" on > Fedora and "apt-get install libslirp-dev" on Debian for example), recompile your QEMU with --enable-slirp, then try again.

[TommyMurphyTM1234]

The title of this PR seems to be misleading?
This change seems to configure QEMU to enable slirp support.
But the package still needs to be installed separately?
Slirp is no longer a submodule of QEMU since 7.2.0 as per the release notes that I linked above.

[cmuellner]

Are you sure that this is needed? Afaik that's automatically discovered and enabled if the library is available. So, I believe the only thing needed is to install libslirp-dev or libslirp-devel.

I think it's not enough, it complains:

network backend 'user' is not compiled into this binary

And as the doc says, we still need to enable it explicitly:

... this might be caused by the missing "user" mode backend. In that case, please install libslirp first ("dnf install libslirp-devel" on > Fedora and "apt-get install libslirp-dev" on Debian for example), recompile your QEMU with --enable-slirp, then try again.

I've built QEMU here without any config flags and it states the following during the build process:

[...]
  Network backends                                                                                                                                                                                                                            
    AF_XDP support                               : NO                                                                                                                                                                                         
    slirp support                                : YES 4.7.0                                                                                                                                                                                  
    vde support                                  : NO                                                                                                                                                                                         
    netmap support                               : NO                                                                                                                                                                                         
    l2tpv3 support                               : YES
[...]

And the built qemu-system-riscv64 can be used with -netdev user,id=net1 -device virtio-net-device,netdev=net1.

I think that --enable-slirp is default if libsirp is found during configuration.

[wangpc-pp]

The title of this PR seems to be misleading?

Yeah, I will change it.

This change seems to configure QEMU to enable slirp support.
But the package still needs to be installed separately?

Yes, slirp supoprt is added and we will build libslirp.so too after a

Slirp is no longer a submodule of QEMU since 7.2.0 as per the release notes that I linked above.

Are you sure that this is needed? Afaik that's automatically discovered and enabled if the library is available. So, I believe the only thing needed is to install libslirp-dev or libslirp-devel.

I think it's not enough, it complains:

network backend 'user' is not compiled into this binary

And as the doc says, we still need to enable it explicitly:

... this might be caused by the missing "user" mode backend. In that case, please install libslirp first ("dnf install libslirp-devel" on > Fedora and "apt-get install libslirp-dev" on Debian for example), recompile your QEMU with --enable-slirp, then try again.

I've built QEMU here without any config flags and it states the following during the build process:

[...]
  Network backends                                                                                                                                                                                                                            
    AF_XDP support                               : NO                                                                                                                                                                                         
    slirp support                                : YES 4.7.0                                                                                                                                                                                  
    vde support                                  : NO                                                                                                                                                                                         
    netmap support                               : NO                                                                                                                                                                                         
    l2tpv3 support                               : YES
[...]

And the built qemu-system-riscv64 can be used with -netdev user,id=net1 -device virtio-net-device,netdev=net1.

I think that --enable-slirp is default if libsirp is found during configuration.

Yeah, you're right. Maybe we should add it to README.td?

[cmuellner]

And the built qemu-system-riscv64 can be used with -netdev user,id=net1 -device virtio-net-device,netdev=net1.
I think that --enable-slirp is default if libsirp is found during configuration.

Yeah, you're right. Maybe we should add it to README.td?

Fine for me.
If so, then please also make sure it is installed in the CI/CD script.

[cmuellner]

LGTM

[cmuellner]

Thanks!