fix(vfs/posix): various vfs fixes for Linux

While trying to find what could possibly cause files on disk to become corrupted
on Linux I started going through the VFS implementation for Linux and noticed
a few issues.

This fixes a few issues here:

Read/ReadBulk/Write don't try to loop until all of their bytes are written

RenameFile returns `0` on success, while we were checking if it was successful
by checking if it was `!= 0`

GetLength was still reading the buf even though there isn't valid data in it.

See:

https://man7.org/linux/man-pages/man2/write.2.html
https://man7.org/linux/man-pages/man2/read.2.html
https://man7.org/linux/man-pages/man2/pread.2.html
https://man7.org/linux/man-pages/man3/fstat.3p.html
https://man7.org/linux/man-pages/man2/rename.2.html

Author: AvarianKnight

code/components/vfs-impl-server/src/PlatformDevice.Posix.cpp

@@ -63,27 +63,90 @@ size_t LocalDevice::Read(THandle handle, void* outBuffer, size_t size)
 {
 	assert(handle != Device::InvalidHandle);
 
-	ssize_t bytesRead = read(static_cast<int>(handle), outBuffer, size);
+	size_t totalBytesRead = 0;
 
-	return (bytesRead < 0) ? -1 : static_cast<size_t>(bytesRead);
+	while (totalBytesRead < size)
+	{
+		ssize_t bytesRead = read(static_cast<int>(handle), outBuffer + totalBytesRead, size - totalBytesRead);
+		if (bytesRead < 0)
+		{
+			// we got interrupted, we should retry our read
+			if (errno == EINTR)
+			{
+				continue;
+			}
+
+			// TODO: Figure out if we want to return what we have or if we should return -1 here?
+			return (totalBytesRead > 0) ? totalBytesRead : -1;
+		}
+
+		if (bytesRead == 0)
+		{
+			break;
+		}
+
+		totalBytesRead += static_cast<size_t>(bytesRead);
+	}
+
+	return totalBytesRead;
 }
 
 size_t LocalDevice::ReadBulk(THandle handle, uint64_t ptr, void* outBuffer, size_t size)
 {
 	assert(handle != Device::InvalidHandle);
 
-	ssize_t bytesRead = pread(static_cast<int>(handle), outBuffer, size, static_cast<off_t>(ptr));
+	size_t totalBytesRead = 0;
+
+	while (totalBytesRead < size)
+	{
+		ssize_t bytesRead = pread(static_cast<int>(handle), outBuffer + totalBytesRead, size - totalBytesRead);
+		if (bytesRead < 0)
+		{
+			// we got interrupted, we should retry our pread
+			if (errno == EINTR)
+			{
+				continue;
+			}
+
+			// TODO: Figure out if we want to return what we have or if we should return -1 here?
+			return (totalBytesRead > 0) ? totalBytesRead : -1;
+		}
+
+		if (bytesRead == 0)
+		{
+			break;
+		}
+
+		totalBytesRead += static_cast<size_t>(bytesRead);
+	}
 
-	return (bytesRead < 0) ? -1 : static_cast<size_t>(bytesRead);
+	return totalBytesRead;
 }
 
 size_t LocalDevice::Write(THandle handle, const void* buffer, size_t size)
 {
 	assert(handle != Device::InvalidHandle);
 
-	ssize_t bytesWritten = write(static_cast<int>(handle), buffer, size);
+	size_t totalBytesWritten = 0;
+
+	while (totalBytesWritten < size)
+	{
+		ssize_t bytesWritten = write(static_cast<int>(handle), buffer + totalWritten, size - totalBytesWritten);
+		if (bytesWritten < 0)
+		{
+			// if we got interrupted we should retry our write
+			if (errno == EINTR)
+			{
+				continue;
+			}
+
+			return -1;
+		}
+		
+		totalBytesWritten += static_cast<size_t>(bytesWritten);
+	}
 
-	return (bytesWritten < 0) ? -1 : static_cast<size_t>(bytesWritten);
+	return totalBytesWritten;
 }
 
 size_t LocalDevice::WriteBulk(THandle handle, uint64_t ptr, const void* buffer, size_t size)