Function BufFileWrite

src/backend/storage/file/buffile.c:823–877

* BufFileWrite * * Like fwrite() except we assume 1-byte element size and report errors via * ereport(). */

 * ereport().
 */
void
BufFileWrite(BufFile *file, void *ptr, size_t size)
{
	size_t		nthistime;

	Assert(!file->readOnly);

	SIMPLE_FAULT_INJECTOR("workfile_write_failure");

	switch (file->state)
	{
		case BFS_RANDOM_ACCESS:
		case BFS_SEQUENTIAL_WRITING:
			break;

		case BFS_COMPRESSED_WRITING:
			BufFileDumpCompressedBuffer(file, ptr, size);
			return;

		case BFS_SEQUENTIAL_READING:
		case BFS_COMPRESSED_READING:
			elog(ERROR, "cannot write to sequential BufFile after reading");
	}

	while (size > 0)
	{
		if (file->pos >= BLCKSZ)
		{
			/* Buffer full, dump it out */
			if (file->dirty)
				BufFileDumpBuffer(file);
			else
			{
				/* Hmm, went directly from reading to writing? */
				file->curOffset += file->pos;
				file->pos = 0;
				file->nbytes = 0;
			}
		}

		nthistime = BLCKSZ - file->pos;
		if (nthistime > size)
			nthistime = size;
		Assert(nthistime > 0);

		memcpy(file->buffer.data + file->pos, ptr, nthistime);

		file->dirty = true;
		file->pos += nthistime;
		if (file->nbytes < file->pos)
			file->nbytes = file->pos;
		ptr = (void *) ((char *) ptr + nthistime);
		size -= nthistime;
	}
}

/*
 * BufFileFlush