fix: Improve validation for system shared memory register

[pskiran1]

What does the PR do?

This PR is an enhancement for #8273.
Previously, users could bypass validation by using a leading slash in shm_key, such as "/triton_python_backend_shm_region_my_test_shm_key", "///triton_python_backend_shm_region_my_test_shm_key"

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[pskiran1]

This validation is optional; if we skip it, the code will fail later.
Since we need to check for slashes in this function, I added this validation to return error early.

[yinggeh]

Left comment

[yinggeh]

Is ./triton_python_backend_shm_region_my_test_shm_keyanother corner case?

[pskiran1]

Is ./triton_python_backend_shm_region_my_test_shm_keyanother corner case?

Thank you for your note. I verified it, and it’s not an issue. It bypasses the validation, but the server still rejects it because it does not read the PB SHM and treats it as a different one.

# curl -X POST "localhost:8000/v2/systemsharedmemory/region/mytestmem/register" -H "Content-Type: application/json" -d '{"key": "./triton_python_backend_shm_region_858ece88-9702-44ea-b1e7-5c4ee9258c1f", "byte_size":100000}' | jq
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   224  100   122  100   102   120k   100k --:--:-- --:--:-- --:--:--  218k
{
  "error": "Unable to open shared memory region: './triton_python_backend_shm_region_858ece88-9702-44ea-b1e7-5c4ee9258c1f'"
}

If we try to create an shm handle using the client, POSIX shm_open also rejects it with an error.

File "/usr/local/lib/python3.12/dist-packages/tritonclient/utils/shared_memory/__init__.py", line 82, in create_shared_memory_region
    shm_handle._mpsm_handle = mpshm.SharedMemory(shm_key)
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/multiprocessing/shared_memory.py", line 104, in __init__
    self._fd = _posixshmem.shm_open(
               ^^^^^^^^^^^^^^^^^^^^^
OSError: [Errno 22] Invalid argument: '/./triton_python_backend_shm_region_faa7f1c0-4b33-47a5-a893-d1b3e5178ad4