[PATCH v2 1/1] python/machine: Fix AF_UNIX path too long on macOS

[Peter Delevoryas]

On macOS, private $TMPDIR's are the default. These $TMPDIR's are
generated from a user's unix UID and UUID [1], which can create a
relatively long path:

    /var/folders/d7/rz20f6hd709c1ty8f6_6y_z40000gn/T/

QEMU's avocado tests create a temporary directory prefixed by
"avo_qemu_sock_", and create QMP sockets within _that_ as well.
The QMP socket is unnecessarily long, because a temporary directory
is created for every QEMUMachine object.

    /avo_qemu_sock_uh3w_dgc/qemu-37331-10bacf110-monitor.sock

The path limit for unix sockets on macOS is 104: [2]

    /*
     * [XSI] Definitions for UNIX IPC domain.
     */
    struct  sockaddr_un {
        unsigned char   sun_len;        /* sockaddr len including null */
        sa_family_t     sun_family;     /* [XSI] AF_UNIX */
        char            sun_path[104];  /* [XSI] path name (gag) */
    };

This results in avocado tests failing on macOS because the QMP unix
socket can't be created, because the path is too long:

    ERROR| Failed to establish connection: OSError: AF_UNIX path too long

This change reduces the size of both paths, and removes the unique
identification information from the socket name, since it seems to be
unnecessary.

This commit produces paths like the following:

    pdel@pdel-mbp:/var/folders/d7/rz20f6hd709c1ty8f6_6y_z40000gn/T
    $ tree qemu*
    qemu_oc7h7f3u
    ├── qmp-console.sock
    └── qmp-monitor.sock

[1] 
https://apple.stackexchange.com/questions/353832/why-is-mac-osx-temp-directory-in-weird-path
[2] /Library/Developer/CommandLineTools/SDKs/MacOSX12.3.sdk/usr/include/sys/un.h

Signed-off-by: Peter Delevoryas <pe...@pjd.dev>
---
 python/qemu/machine/machine.py         | 2 +-
 tests/avocado/avocado_qemu/__init__.py | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/python/qemu/machine/machine.py b/python/qemu/machine/machine.py
index 37191f433b..b1823966b3 100644
--- a/python/qemu/machine/machine.py
+++ b/python/qemu/machine/machine.py
@@ -157,7 +157,7 @@ def __init__(self,
         self._wrapper = wrapper
         self._qmp_timer = qmp_timer
 
-        self._name = name or f"qemu-{os.getpid()}-{id(self):02x}"
+        self._name = name or "qmp"
         self._temp_dir: Optional[str] = None
         self._base_temp_dir = base_temp_dir
         self._sock_dir = sock_dir
diff --git a/tests/avocado/avocado_qemu/__init__.py 
b/tests/avocado/avocado_qemu/__init__.py
index ed4853c805..43b8c8848c 100644
--- a/tests/avocado/avocado_qemu/__init__.py
+++ b/tests/avocado/avocado_qemu/__init__.py
@@ -296,7 +296,7 @@ def require_accelerator(self, accelerator):
                         "available" % accelerator)
 
     def _new_vm(self, name, *args):
-        self._sd = tempfile.TemporaryDirectory(prefix="avo_qemu_sock_")
+        self._sd = tempfile.TemporaryDirectory(prefix="qemu_")
         vm = QEMUMachine(self.qemu_bin, base_temp_dir=self.workdir,
                          sock_dir=self._sd.name, log_dir=self.logdir)
         self.log.debug('QEMUMachine "%s" created', name)
-- 
2.37.0