libssh-0.8 is detected as 0.7

[Philippe Mathieu-Daudé]

QEMU consumes the library and its configure script use the libssh pkg-config cflags.
The it checks if ssh_get_server_publickey() is present and assume it is a libssh-0.8 based.

Ubuntu libssh is not based on upstream 0.8 but on the 0.7 branch, with commit bbd052202 cherry-picked. This commit adds the ssh_get_server_publickey() function that QEMU uses to check 0.8 compatibility.
Now commit 963c46e4f is present in libssh-0.8 but has not been cherry-picked by Ubuntu, so QEMU fails at compiling because the ssh_known_hosts_e enums this commit introduced are missing.

QEMU tracker is https://bugs.launchpad.net/qemu/+bug/1838763

How to reproduce:

- install libssh-dev

- try to build QEMU 4.1 (sources from https://www.qemu.org/download/#source)

$ ./configure
...
libssh support yes
...

$ make
...
  CC block/ssh.o
block/ssh.c: In function 'check_host_key_knownhosts':
block/ssh.c:281:28: error: storage size of 'state' isn't known
     enum ssh_known_hosts_e state;
                            ^~~~~
block/ssh.c:289:13: error: implicit declaration of function 'ssh_session_is_known_server' [-Werror=implicit-function-declaration]
     state = ssh_session_is_known_server(s->session);
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~
block/ssh.c:289:13: error: nested extern declaration of 'ssh_session_is_known_server' [-Werror=nested-externs]
block/ssh.c:293:10: error: 'SSH_KNOWN_HOSTS_OK' undeclared (first use in this function); did you mean 'SSH_OPTIONS_HOSTKEYS'?
     case SSH_KNOWN_HOSTS_OK:
          ^~~~~~~~~~~~~~~~~~
          SSH_OPTIONS_HOSTKEYS
block/ssh.c:293:10: note: each undeclared identifier is reported only once for each function it appears in
block/ssh.c:297:10: error: 'SSH_KNOWN_HOSTS_CHANGED' undeclared (first use in this function); did you mean 'SSH_KNOWN_HOSTS_OK'?
     case SSH_KNOWN_HOSTS_CHANGED:
          ^~~~~~~~~~~~~~~~~~~~~~~
          SSH_KNOWN_HOSTS_OK
block/ssh.c:301:48: error: 'SSH_PUBLICKEY_HASH_SHA256' undeclared (first use in this function); did you mean 'SSH_PUBLICKEY_HASH_SHA1'?
             r = ssh_get_publickey_hash(pubkey, SSH_PUBLICKEY_HASH_SHA256,
                                                ^~~~~~~~~~~~~~~~~~~~~~~~~
                                                SSH_PUBLICKEY_HASH_SHA1
block/ssh.c:307:27: error: implicit declaration of function 'ssh_get_fingerprint_hash'; did you mean 'ssh_get_pubkey_hash'? [-Werror=implicit-function-declaration]
             fingerprint = ssh_get_fingerprint_hash(SSH_PUBLICKEY_HASH_SHA256,
                           ^~~~~~~~~~~~~~~~~~~~~~~~
                           ssh_get_pubkey_hash
block/ssh.c:307:27: error: nested extern declaration of 'ssh_get_fingerprint_hash' [-Werror=nested-externs]
block/ssh.c:324:10: error: 'SSH_KNOWN_HOSTS_OTHER' undeclared (first use in this function); did you mean 'SSH_KNOWN_HOSTS_OK'?
     case SSH_KNOWN_HOSTS_OTHER:
          ^~~~~~~~~~~~~~~~~~~~~
          SSH_KNOWN_HOSTS_OK
block/ssh.c:329:10: error: 'SSH_KNOWN_HOSTS_UNKNOWN' undeclared (first use in this function); did you mean 'SSH_KNOWN_HOSTS_CHANGED'?
     case SSH_KNOWN_HOSTS_UNKNOWN:
          ^~~~~~~~~~~~~~~~~~~~~~~
          SSH_KNOWN_HOSTS_CHANGED
block/ssh.c:333:10: error: 'SSH_KNOWN_HOSTS_NOT_FOUND' undeclared (first use in this function); did you mean 'SSH_KNOWN_HOSTS_UNKNOWN'?
     case SSH_KNOWN_HOSTS_NOT_FOUND:
          ^~~~~~~~~~~~~~~~~~~~~~~~~
          SSH_KNOWN_HOSTS_UNKNOWN
block/ssh.c:337:10: error: 'SSH_KNOWN_HOSTS_ERROR' undeclared (first use in this function); did you mean 'SSH_KNOWN_HOSTS_OTHER'?
     case SSH_KNOWN_HOSTS_ERROR:
          ^~~~~~~~~~~~~~~~~~~~~
          SSH_KNOWN_HOSTS_OTHER
block/ssh.c:281:28: error: unused variable 'state' [-Werror=unused-variable]
     enum ssh_known_hosts_e state;
                            ^~~~~
cc1: all warnings being treated as errors
rules.mak:69: recipe for target 'block/ssh.o' failed
make: *** [block/ssh.o] Error 1

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: libssh-dev 0.8.0~20170825.94fa1e38-1ubuntu0.2
Uname: Linux 5.2.17-200.fc30.x86_64 x86_64
ApportVersion: 2.20.9-0ubuntu7.7
Architecture: amd64
Date: Wed Oct 9 18:21:25 2019
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
SourcePackage: libssh
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.