File s390-tools-sles11sp2-zipl-flush-cache.patch of Package s390-tools

Subject: [PATCH] [BZ 85124] zipl: Flush disk buffers before installing IPL record
From: Stefan Haberland <stefan.haberland@de.ibm.com>

Description:  zipl: Flush disk buffers before installing IPL record
Symptom:      Running zipl on an FBA DASD may cause a previously initialized
              physical volume on the partition to be no longer recognized by
              LVM.
Problem:      The Linux kernel maintains caches for block devices in 
              granularity of pages (4096 bytes). A disk and its partitions are
              represented by separate block devices. As a result, the same area
              on disk may be represented by entries in both the disk and 
              partition cache.
              The following sequence of block device access requests can
              lead to inconsistent cache contents for the first 4096 bytes on
              an FBA DASD:
                 A) read block 0 from DISK (done for example by the kernel
                    during partition detection)
                 B) write block 0 to PARTITION (done for example by pvcreate
                    when initializing the partition as physical volume)
              When zipl is run, it writes the IPL record to block 0 on DISK.
              Since the IPL record is less than 4096 bytes but a write to the
              disk device is ultimately done in multiples of the page size, the
              remaining data is taken from the disk block device cache which
              contains the contents resulting from A). As a result, the effects
              of B) are effectively undone on disk.
Solution:     Flush the cache for the disk and partition block devices before
              installing the IPL record.
Reproduction: A) read block 0 from DISK (done for example by the kernel during
                 partition detection)
              B) write block 0 to PARTITION (done for example by pvcreate when
                 initializing the partition as physical volume)
              C) run zipl
Problem-ID:   85124
---
 zipl/src/install.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/zipl/src/install.c
+++ b/zipl/src/install.c
@@ -30,6 +30,9 @@
 #include "error.h"
 #include "misc.h"
 
+/* From linux/fs.h */
+#define BLKFLSBUF	_IO(0x12, 97)
+
 
 /* Types of SCSI disk layouts */
 enum scsi_layout {
@@ -311,6 +314,14 @@ install_bootloader(const char* device, d
 			   device);
 		return -1;
 	}
+	/* Ensure that potential cache inconsistencies between disk and
+	 * partition are resolved by flushing the corresponding buffers. */
+	if (!dry_run) {
+		if (ioctl(fd, BLKFLSBUF)) {
+			fprintf(stderr, "Warning: Could not flush disk "
+				"caches.\n");
+		}
+	}
 	/* Call disk specific install functions */
 	rc = -1;
 	switch (info->type) {