[libc-commits] [libc] [libc] Add `shm_open/shm_unlink` (PR #84974)

[via libc-commits]

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@@ -0,0 +1,51 @@
+//===---------- Shared implementations for shm_open/shm_unlink ------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/array.h"
+#include "src/__support/CPP/optional.h"
+#include "src/__support/CPP/string_view.h"
+#include "src/errno/libc_errno.h"
+#include "src/string/memchr.h"
+#include "src/string/memcpy.h"
+#include <asm/errno.h>
+#include <linux/limits.h>
+
+namespace LIBC_NAMESPACE {
+
+LIBC_INLINE_VAR constexpr cpp::string_view SHM_PREFIX = "/dev/shm/";
+using SHMPath = cpp::array<char, NAME_MAX + SHM_PREFIX.size() + 1>;
+
+LIBC_INLINE cpp::optional<SHMPath> get_shm_name(cpp::string_view name) {
+  // trim leading slashes
+  size_t offset = name.find_first_not_of('/');
+  if (offset == cpp::string_view::npos) {
+    libc_errno = EINVAL;
+    return cpp::nullopt;
+  }
+  name = name.substr(offset);
+
+  // check the name
+  if (name.size() > NAME_MAX) {
+    libc_errno = ENAMETOOLONG;
+    return cpp::nullopt;
+  }
+  if (name == "." || name == ".." ||
+      memchr(name.data(), '/', name.size()) != nullptr) {
+    libc_errno = EINVAL;
+    return cpp::nullopt;
+  }
+
+  // prepend the prefix
+  SHMPath buffer;
+  memcpy(buffer.data(), SHM_PREFIX.data(), SHM_PREFIX.size());
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lntue wrote:

I think we do have some internal `memcpy` so that you don't have to depend on `memcpy` entry points.  You might need to add a similar one for `memchr` if we don't have it yet.  @michaelrj-google and @gchatelet 

https://github.com/llvm/llvm-project/pull/84974