[llvm][cas] Fix error handling of posix_fallocate

The posix_fallocate function returns an error code directly and not via
errno, and on older POSIX versions it may return EINVAL in places it
should return ENOTSUP (in practice, seen on FreeBSD).

(cherry picked from commit c8f75c6)

Author: benlangmuir

llvm/lib/CAS/OnDiskCommon.cpp

@@ -11,6 +11,7 @@
 #include "llvm/Config/config.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/Process.h"
+#include <limits>
 #include <mutex>
 #include <optional>
 #include <thread>
@@ -115,16 +116,25 @@ cas::ondisk::tryLockFileThreadSafe(int FD, std::chrono::milliseconds Timeout,
 }
 
 Expected<size_t> cas::ondisk::preallocateFileTail(int FD, size_t CurrentSize, size_t NewSize) {
-  auto CreateErrorFromErrno = [&]() -> Expected<size_t> {
-    std::error_code EC = errnoAsErrorCode();
+  auto CreateError = [&](std::error_code EC) -> Expected<size_t> {
     if (EC == std::errc::not_supported)
       // Ignore ENOTSUP in case the filesystem cannot preallocate.
       return NewSize;
+#if defined(HAVE_POSIX_FALLOCATE)
+    if (EC == std::errc::invalid_argument &&
+        CurrentSize < NewSize && // len > 0
+        NewSize < std::numeric_limits<off_t>::max()) // 0 <= offset, len < max
+      // Prior to 2024, POSIX required EINVAL for cases that should be ENOTSUP,
+      // so handle it the same as above if it is not one of the other ways to
+      // get EINVAL.
+      return NewSize;
+#endif
     return createStringError(EC, "failed to allocate to CAS file: " + EC.message());
   };
 #if defined(HAVE_POSIX_FALLOCATE)
-  if (posix_fallocate(FD, CurrentSize, NewSize - CurrentSize))
-    return CreateErrorFromErrno();
+  // Note: posix_fallocate returns its error directly, not via errno.
+  if (int Err = posix_fallocate(FD, CurrentSize, NewSize - CurrentSize))
+    return CreateError(std::error_code(Err, std::generic_category()));
   return NewSize;
 #elif defined(__APPLE__)
   fstore_t FAlloc;
@@ -134,7 +144,7 @@ Expected<size_t> cas::ondisk::preallocateFileTail(int FD, size_t CurrentSize, si
   FAlloc.fst_length = NewSize - CurrentSize;
   FAlloc.fst_bytesalloc = 0;
   if (fcntl(FD, F_PREALLOCATE, &FAlloc))
-    return CreateErrorFromErrno();
+    return CreateError(errnoAsErrorCode());
   assert(CurrentSize + FAlloc.fst_bytesalloc >= NewSize);
   return CurrentSize + FAlloc.fst_bytesalloc;
 #else