Set of offset-based APIs for thread-safe file IO

[adamsitnik]

I've moved all the logic responsible for opening and initializing SafeFileHandle to SafeFileHandle. A lot of duplicated code (mostly for initializing ThreadPoolBinding) got removed. On Unix, it's also now much more clear how many syscalls we perform to just open a file.

Other changes:

• Instead of using NtCreateFile for cases when preallocationSize was specified and CreateFileW when not, I've followed @JeremyKuhne suggestion and switched to using NtCreateFile only. This has simplified the code and provided some minor perf gain. I've discovered a bug in the previous implementation (related to DesiredAccess.DELETE) fixed it, and added a test
• On Unix, I've realized that once we call fstat() to ensure that a given file is not a directory we can also determine whether a given file is seekable or not. This has removed one syscall for the initialization of CanSeek.

Fixes #24847

@carlossanlop @Jozkee @stephentoub PTAL. Once this PR is merged, I would like to finally publish the .NET Blog post.

cc @alexbudmsft

[stephentoub]

Nit: nuint

[stephentoub]

Let's open an issue in runtime for now and include the link here.

[stephentoub]

Should we move them to here?

runtime/src/libraries/Native/Unix/System.Native/pal_networking.c

Lines 163 to 168 in c87354c

	// We require that IOVector have the same layout as iovec.
	c_static_assert(sizeof(IOVector) == sizeof(iovec));
	c_static_assert(sizeof_member(IOVector, Base) == sizeof_member(iovec, iov_base));
	c_static_assert(offsetof(IOVector, Base) == offsetof(iovec, iov_base));
	c_static_assert(sizeof_member(IOVector, Count) == sizeof_member(iovec, iov_len));
	c_static_assert(offsetof(IOVector, Count) == offsetof(iovec, iov_len));

[janvorli]

@adamsitnik this change has broken my local build on Apple Silicon. It fails with:

/Users/janvorli/git/runtime2/src/libraries/Native/Unix/System.Native/pal_io.c:1491:21: error: implicit declaration of function 'preadv' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
      while ((count = preadv(fileDescriptor, (struct iovec*)vectors, (int)vectorCount, (off_t)fileOffset)) < 0 && errno == EINTR);
                      ^
  /Users/janvorli/git/runtime2/src/libraries/Native/Unix/System.Native/pal_io.c:1531:21: error: implicit declaration of function 'pwritev' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
      while ((count = pwritev(fileDescriptor, (struct iovec*)vectors, (int)vectorCount, (off_t)fileOffset)) < 0 && errno == EINTR);
                      ^
  2 errors generated.

However the checks for HAVE_PREADV and HAVE_PWRITEV in the configuration have succeeded. I suspect that the functions have moved to a different header file in recent SDK and the pal_io.c doesn't include it. But I am not sure yet.

[janvorli]

Btw, this was a clean build after git clean -xdf.

[janvorli]

I can see that the preadv / pwritew in my SDK are available only if:
#if (!defined(_POSIX_C_SOURCE) && !defined(_XOPEN_SOURCE)) || defined(_DARWIN_C_SOURCE)
Looking at the compiler options for the pal_io.c, we set the _XOPEN_SOURCE, so that blocks the preadv / pwritev.

[filipnavara]

@janvorli I suspect it may be the macOS version passed to the compiler as minimum version. The APIs were added in macOS 11. If the cake checks don't pass the target minimum macOS version it will likely use the latest and find the APIs. The actual compilation likely targets older macOS version and either compiles against older SDK or the SDK hides the symbols.

Nevermind, I see you already checked the headers meanwhile. Also I realized that the Apple Silicon version may target macOS 11 as minimum (unlike the x64 one).

[janvorli]

Adding _DARWIN_C_SOURCE definition for the System.Native (for OSX target) fixed the build for me.