Reject unsupported append mode

cpp/include/cucim/filesystem/cufile_driver.h

@@ -35,9 +35,10 @@ bool EXPORT_VISIBLE is_gds_available();
  * - "r": O_RDONLY
  * - "r+": O_RDWR
  * - "w": O_RDWR | O_CREAT | O_TRUNC
- * - "a": O_RDWR | O_CREAT
  * In addition to above flags, the method append O_CLOEXEC and O_DIRECT by default.
  *
+ * Append mode ("a") is not supported because CuFileDriver exposes explicit-offset pread()/pwrite() APIs.
+ *
  * The following is optional flags that can be added to above string:
  * - 'p': Use POSIX APIs only (first try to open with O_DIRECT). It does not use GDS.
  * - 'n': Do not add O_DIRECT flag.
@@ -56,6 +57,7 @@ std::shared_ptr<CuFileDriver> EXPORT_VISIBLE open(const char* file_path, const c
  * Open file with existing file descriptor.
  *
  * @param fd A file descriptor. To use GDS, fd needs to be opened with O_DIRECT flag.
+ *           File descriptors opened with O_APPEND are not supported.
  * @param no_gds true if you do not want to use GDS. Default value is `false`.
  * @param use_mmap true if you want to use memory-mapped IO. This flag is supported only for the read-only file descriptor. Default value is `false`.
  * @return A std::shared_ptr object of CuFileDriver.

cpp/src/filesystem/cufile_driver.cpp

@@ -30,6 +30,8 @@ namespace cucim::filesystem
 {
 static constexpr unsigned int PAGE_SIZE = 4096;
 static constexpr uint64_t DEFAULT_MAX_CACHE_SIZE = 128 << 20; // 128MiB
+static constexpr char kAppendModeUnsupportedMessage[] =
+    "Append mode is not supported because CuFileDriver uses explicit-offset pread()/pwrite() semantics.";
 static CuFileStub s_cufile_stub;
 static CuFileDriverInitializer s_cufile_initializer;
 thread_local static CuFileDriverCache s_cufile_cache;
@@ -76,9 +78,6 @@ static int get_file_flags(const char* flags)
     case 'w':
         file_flags = O_RDWR | O_CREAT | O_TRUNC;
         break;
-    case 'a':
-        file_flags = O_RDWR | O_CREAT;
-        break;
     default:
         return -1;
     }
@@ -96,6 +95,11 @@ bool is_gds_available()
 
 std::shared_ptr<CuFileDriver> open(const char* file_path, const char* flags, mode_t mode)
 {
+    if (flags != nullptr && flags[0] == 'a')
+    {
+        throw std::invalid_argument(kAppendModeUnsupportedMessage);
+    }
+
     bool use_o_direct = true;
     bool no_gds = false;
     bool use_mmap = false;
@@ -189,6 +193,10 @@ CuFileDriver::CuFileDriver(int fd, bool no_gds, bool use_mmap, const char* file_
     {
         throw std::runtime_error(fmt::format("[Error] fcntl failed for fd {} ({})", fd, std::strerror(errno)));
     }
+    if (flags & O_APPEND)
+    {
+        throw std::invalid_argument(kAppendModeUnsupportedMessage);
+    }
     file_flags_ = flags;
 
     FileHandleType file_type = (flags & O_DIRECT) ? FileHandleType::kPosixODirect : FileHandleType::kPosix;

cpp/tests/test_cufile.cpp

@@ -12,6 +12,7 @@
 #include <chrono>
 #include <cstdlib>
 #include <fcntl.h>
+#include <stdexcept>
 #include <unistd.h>
 #include <string_view>
 // Test
@@ -58,6 +59,19 @@ static void create_test_file(const char* file_name, int size)
     close(fd);
 }
 
+TEST_CASE("Append mode should be rejected", "[test_cufile.cpp]")
+{
+    std::string output_file = fmt::format("{}/test_cufile_append.raw", g_config.temp_folder);
+    create_test_file(output_file.c_str(), 32);
+
+    REQUIRE_THROWS_AS(cucim::filesystem::open(output_file.c_str(), "a"), std::invalid_argument);
+
+    int append_fd = ::open(output_file.c_str(), O_RDWR | O_APPEND);
+    REQUIRE(append_fd >= 0);
+    REQUIRE_THROWS_AS(cucim::filesystem::open(append_fd, true, false), std::invalid_argument);
+    ::close(append_fd);
+}
+
 TEST_CASE("Verify libcufile usage", "[test_cufile.cpp]")
 {
     cudaError_t cuda_status;

python/pybind11/filesystem/cufile_pydoc.h

@@ -16,6 +16,7 @@ Constructor of CuFileDriver.
 
 Args:
     fd: A file descriptor (in `int` type) which is available through `os.open()` method.
+        File descriptors opened with `os.O_APPEND` are not supported.
     no_gds: If True, use POSIX APIs only even when GDS can be supported for the file.
     use_mmap: If True, use memory-mapped IO. This flag is supported only for the read-only file descriptor. Default value is `False`.
     file_path: A file path for the file descriptor. It would retrieve the absolute file path of the file descriptor if not specified.

python/pybind11/filesystem/filesystem_pydoc.h

@@ -31,10 +31,10 @@ Open file with specific flags and mode.
 
 - "w": os.O_RDWR | os.O_CREAT | os.O_TRUNC
 
-- "a": os.O_RDWR | os.O_CREAT
-
 In addition to above flags, the method append os.O_CLOEXEC and os.O_DIRECT by default.
 
+Append mode ("a") is not supported because CuFileDriver exposes explicit-offset pread()/pwrite() APIs.
+
 The following is optional flags that can be added to above string:
 
 - 'p': Use POSIX APIs only (first try to open with O_DIRECT). It does not use GDS.