[libc-commits] [libc] [libc] Implement fallocate (PR #222843)

[Pavel Labath via libc-commits]

================
@@ -0,0 +1,48 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file contains the declaration of the fallocate, which is the
+/// base syscall wrapper for all fallocate dependent calls.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_FALLOCATE_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_SYSCALL_WRAPPERS_FALLOCATE_H
+
+#include "hdr/errno_macros.h"
+#include "hdr/types/off_t.h"
+#include "src/__support/CPP/bit.h"
+#include "src/__support/CPP/limits.h"
+#include "src/__support/OSUtil/linux/syscall.h" // For syscall_checked
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include <sys/syscall.h> // For syscall numbers
+
+namespace LIBC_NAMESPACE_DECL {
+namespace linux_syscalls {
+
+LIBC_INLINE ErrorOr<int> fallocate(int fd, int mode, off_t offset, off_t size) {
+  if constexpr (sizeof(long) == sizeof(uint32_t) &&
+                sizeof(off_t) == sizeof(uint64_t)) {
+    uint64_t offset_bits = cpp::bit_cast<uint64_t>(offset);
+    long offset_low = static_cast<long>(offset_bits & UINT32_MAX);
+    long offset_high = static_cast<long>(offset_bits >> 32);
+    uint64_t len_bits = cpp::bit_cast<uint64_t>(size);
+    long len_low = static_cast<long>(len_bits & UINT32_MAX);
+    long len_high = static_cast<long>(len_bits >> 32);
+    return syscall_checked<int>(SYS_fallocate, fd, mode, offset_low,
+                                offset_high, len_low, len_high);
+  } else
+    return syscall_checked<int>(SYS_fallocate, fd, mode, offset, size);
----------------
labath wrote:

For consistency with the if block.

```suggestion
  } else {
    return syscall_checked<int>(SYS_fallocate, fd, mode, offset, size);
  }
```

https://github.com/llvm/llvm-project/pull/222843