Function dump_write_headers

freebsd/kern/kern_shutdown.c:1485–1543

* Write kernel dump headers at the beginning and end of the dump extent. * Write the kernel dump encryption key after the leading header if we were * configured to do so. */

 * configured to do so.
 */
static int
dump_write_headers(struct dumperinfo *di, struct kerneldumpheader *kdh)
{
#ifdef EKCD
	struct kerneldumpcrypto *kdc;
#endif
	void *buf, *key;
	size_t hdrsz;
	uint64_t extent;
	uint32_t keysize;
	int error;

	hdrsz = sizeof(*kdh);
	if (hdrsz > di->blocksize)
		return (ENOMEM);

#ifdef EKCD
	kdc = di->kdcrypto;
	key = kdc->kdc_dumpkey;
	keysize = kerneldumpcrypto_dumpkeysize(kdc);
#else
	key = NULL;
	keysize = 0;
#endif

	/*
	 * If the dump device has special handling for headers, let it take care
	 * of writing them out.
	 */
	if (di->dumper_hdr != NULL)
		return (di->dumper_hdr(di, kdh, key, keysize));

	if (hdrsz == di->blocksize)
		buf = kdh;
	else {
		buf = di->blockbuf;
		memset(buf, 0, di->blocksize);
		memcpy(buf, kdh, hdrsz);
	}

	extent = dtoh64(kdh->dumpextent);
#ifdef EKCD
	if (kdc != NULL) {
		error = dump_write(di, kdc->kdc_dumpkey, 0,
		    di->mediaoffset + di->mediasize - di->blocksize - extent -
		    keysize, keysize);
		if (error != 0)
			return (error);
	}
#endif

	error = dump_write(di, buf, 0,
	    di->mediaoffset + di->mediasize - 2 * di->blocksize - extent -
	    keysize, di->blocksize);
	if (error == 0)
		error = dump_write(di, buf, 0, di->mediaoffset + di->mediasize -
		    di->blocksize, di->blocksize);
	return (error);