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

[Peter Delevoryas]

I noticed that I can't run any avocado tests on macOS because the QMP
unix socket path is too long:

$ ./configure --target-list=arm-softmmu
$ make
$ make check-avocado AVOCADO_TESTS=tests/avocado/boot_linux_console.py
changing dir to build for /Library/Developer/CommandLineTools/usr/bin/make 
"check-avocado"...
  GIT     ui/keycodemapdb meson tests/fp/berkeley-testfloat-3 
tests/fp/berkeley-softfloat-3 dtc slirp
  AVOCADO tests/avocado
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_virt
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_emcraft_sf2
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_emcraft_sf2
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_raspi2_initrd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_raspi2_initrd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_exynos4210_initrd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_exynos4210_initrd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_cubieboard_initrd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_cubieboard_initrd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_cubieboard_sata
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_cubieboard_sata
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_quanta_gsj
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_quanta_gsj_initrd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_quanta_gsj_initrd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_quanta_gsj_initrd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_orangepi
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_orangepi_initrd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_orangepi_initrd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_orangepi_sd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_orangepi_sd
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_orangepi_bionic_20_08
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_orangepi_uboot_netbsd9
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_orangepi_uboot_netbsd9
Fetching asset from 
tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_ast2600_debian
JOB ID     : 84bd26125345c6f12c92d118e98acde6aacfea57
JOB LOG    : 
/Users/pdel/qemu/build/tests/results/job-2022-07-02T11.24-84bd261/job.log
 (01/16) tests/avocado/boot_linux_console.py:BootLinuxConsole.test_arm_virt: 
ERROR: ConnectError: Failed to establish connection: AF_UNIX path too lo
ng\n    Command: \n     Output: None\n (0.11 s)
Interrupting job (failfast).
RESULTS    : PASS 0 | ERROR 1 | FAIL 0 | SKIP 15 | WARN 0 | INTERRUPT 0 | 
CANCEL 0

The job log shows a backtrace that points to the QMP monitor's unix socket path:

2022-07-02 11:24:05,906 protocol         L0554 DEBUG| Awaiting connection on 
/var/folders/d7/rz20f6hd709c1ty8f6_6y_z40000gn/T/avo_qemu_sock_uh3w_dgc/qemu-37331-10bacf110-monitor.sock
 ...
2022-07-02 11:24:05,907 protocol         L0426 ERROR| Failed to establish 
connection: OSError: AF_UNIX path too long

I think the path limit for unix sockets on macOS might be 104 [1]

/*
 * [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) */
};

The path we're using is exactly 105 characters:

$ python
Python 2.7.10 (default, Jan 19 2016, 22:24:01)
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> len('/var/folders/d7/rz20f6hd709c1ty8f6_6y_z40000gn/T/avo_qemu_sock_uh3w_dgc/qemu-37331-10bacf110-monitor.sock')
105

In this change I removed some of the unnecessary elements of the path, to keep
us under the limit. This seemed like the simplest thing to do, and I imagine
the extra human-readable elements were just added to make it easier to identify
left-over sockets or something else related to debugging.

[1]: 
/Library/Developer/CommandLineTools/SDKs/MacOSX12.3.sdk/usr/include/sys/un.h

Signed-off-by: Peter Delevoryas <peter@pjd.dev>
---
 python/qemu/machine/machine.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/python/qemu/machine/machine.py b/python/qemu/machine/machine.py
index 37191f433b..93451774e3 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 f"{os.getpid()}{id(self):02x}"
         self._temp_dir: Optional[str] = None
         self._base_temp_dir = base_temp_dir
         self._sock_dir = sock_dir
@@ -167,7 +167,7 @@ def __init__(self,
             self._monitor_address = monitor_address
         else:
             self._monitor_address = os.path.join(
-                self.sock_dir, f"{self._name}-monitor.sock"
+                self.sock_dir, f"{self._name}.sock"
             )
 
         self._console_log_path = console_log
-- 
2.37.0