Function ltsReadBlock

src/backend/utils/sort/logtape.c:288–304

* Read a block-sized buffer from the specified block of the underlying file. * * No need for an error return convention; we ereport() on any error. This * module should never attempt to read a block it doesn't know is there. */

 * module should never attempt to read a block it doesn't know is there.
 */
static void
ltsReadBlock(LogicalTapeSet *lts, long blocknum, void *buffer)
{
	size_t		nread;

	if (BufFileSeekBlock(lts->pfile, blocknum) != 0)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not seek to block %ld of temporary file",
						blocknum)));
	nread = BufFileRead(lts->pfile, buffer, BLCKSZ);
	if (nread != BLCKSZ)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not read block %ld of temporary file: read only %zu of %zu bytes",
						blocknum, nread, (size_t) BLCKSZ)));
}

/*
 * Read as many blocks as we can into the per-tape buffer.