Re: [PATCH v4 1/1] python/machine: Fix AF_UNIX path too long on macOS

[Philippe Mathieu-Daudé]

On 10/1/23 09:07, Peter Delevoryas wrote:
> 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

Ah, I'm using this klugde:

  $ TMPDIR=/tmp avocado run ...

> This change resolves by reducing the size of the socket directory prefix
> and the suffix on the QMP and console socket names.
>
> The result is paths like this:
>
>      pdel@pdel-mbp:/var/folders/d7/rz20f6hd709c1ty8f6_6y_z40000gn/T
>      $ tree qemu*
>      qemu_df4evjeq
>      qemu_jbxel3gy
>      qemu_ml9s_gg7
>      qemu_oc7h7f3u
>      qemu_oqb1yf97
>      ├── 10a004050.con
>      └── 10a004050.qmp
>
> [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 <peter@pjd.dev>
> ---
>   python/qemu/machine/machine.py         | 6 +++---
>   tests/avocado/avocado_qemu/__init__.py | 2 +-
>   2 files changed, 4 insertions(+), 4 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>