format_text: Round size written up to multiple of 4096.

Zero-fill metadata up to the next 4096 boundary then write out a
multiple of 4096 bytes to avoid triggering a read-modify-write.

4 files changed, 34 insertions, 10 deletions

diff --git a/WHATS_NEW b/WHATS_NEW
index f8713777b..5fc4cd3d2 100644
--- a/WHATS_NEW
+++ b/WHATS_NEW
@@ -1,5 +1,6 @@
 Version 2.02.177 -
 ====================================
+  When writing text metadata content, use complete 4096 byte blocks.
   Change text format metadata alignment from 512 to 4096 bytes.
   When writing metadata, consistently skip mdas marked as failed.
   Refactor and adjust text format metadata alignment calculation.
diff --git a/lib/format_text/export.c b/lib/format_text/export.c
index e5352376d..1bcaf8369 100644
--- a/lib/format_text/export.c
+++ b/lib/format_text/export.c
@@ -23,6 +23,7 @@
 #include "lvm-version.h"
 #include "toolcontext.h"
 #include "config-util.h"
+#include "layout.h"
 
 #include <stdarg.h>
 #include <time.h>
@@ -1079,7 +1080,12 @@ size_t text_vg_export_raw(struct volume_group *vg, const char *desc, char **buf)
 		goto_out;
 	}
 
-	r = f->data.buf.used + 1;
+	f->data.buf.used += 1;	/* Terminating NUL */
+
+	/* Zero fill up to next alignment boundary */
+	memset(f->data.buf.start + f->data.buf.used, 0, MDA_ALIGNMENT - f->data.buf.used % MDA_ALIGNMENT);
+
+	r = f->data.buf.used;
 	*buf = f->data.buf.start;
 
       out:
diff --git a/lib/format_text/format-text.c b/lib/format_text/format-text.c
index ea31a2f50..1aa91c720 100644
--- a/lib/format_text/format-text.c
+++ b/lib/format_text/format-text.c
@@ -704,11 +704,12 @@ static int _vg_write_raw(struct format_instance *fid, struct volume_group *vg,
 	struct mda_header *mdah;
 	struct pv_list *pvl;
 	int r = 0;
-	uint64_t new_wrap;	/* Number of bytes of new metadata that wrap around to start of buffer */
+	uint64_t new_wrap = 0;	/* Number of bytes of new metadata that wrap around to start of buffer */
 	uint64_t alignment = MDA_ALIGNMENT;
 	int found = 0;
 	int noprecommit = 0;
 	const char *old_vg_name = NULL;
+	uint64_t new_size_rounded;
 
 	/* Ignore any mda on a PV outside the VG. vgsplit relies on this */
 	dm_list_iterate_items(pvl, &vg->pvs) {
@@ -735,6 +736,7 @@ static int _vg_write_raw(struct format_instance *fid, struct volume_group *vg,
 	if (!(mdah = raw_read_mda_header(fid->fmt, &mdac->area, mda_is_primary(mda))))
 		goto_out;
 
+	/* Following space is zero-filled up to the next MDA_ALIGNMENT boundary */
 	if (!fidtc->raw_metadata_buf &&
 	    !(fidtc->raw_metadata_buf_size =
 			text_vg_export_raw(vg, "", &fidtc->raw_metadata_buf))) {
@@ -775,19 +777,33 @@ static int _vg_write_raw(struct format_instance *fid, struct volume_group *vg,
 				  vg->name, dev_name(mdac->area.dev), mdac->rlocn.size, mdah->size - MDA_HEADER_SIZE, rlocn ? rlocn->size : 0);
 			goto out;
 		}
+
+		new_size_rounded = mdac->rlocn.size;
+	} else {
+		/* Round up to a multiple of the new alignment */
+		if (mdac->rlocn.offset + new_size_rounded < mdah->size)
+			new_size_rounded = (mdac->rlocn.size | (alignment - 1)) + 1;
+		else
+			new_size_rounded = mdac->rlocn.size;
 	}
 
-	log_debug_metadata("Writing %s metadata to %s at " FMTu64 " len " FMTu64 " of " FMTu64 " aligned to " FMTu64,
+	log_debug_metadata("Writing %s metadata to %s at " FMTu64 " len " FMTu64 " (rounded to " FMTu64 ") of " FMTu64 " aligned to " FMTu64,
 			    vg->name, dev_name(mdac->area.dev), mdac->area.start +
-			    mdac->rlocn.offset, mdac->rlocn.size - new_wrap, mdac->rlocn.size, alignment);
+			    mdac->rlocn.offset, mdac->rlocn.size - new_wrap, new_size_rounded, mdac->rlocn.size, alignment);
 
-	/* Write text out, circularly */
-	if (!dev_write(mdac->area.dev, mdac->area.start + mdac->rlocn.offset,
-		       (size_t) (mdac->rlocn.size - new_wrap), MDA_CONTENT_REASON(mda_is_primary(mda)),
-		       fidtc->raw_metadata_buf))
-		goto_out;
+	if (!new_wrap) {
+		/* Write text out, in alignment-sized blocks */
+		if (!dev_write(mdac->area.dev, mdac->area.start + mdac->rlocn.offset,
+			       (size_t) new_size_rounded, MDA_CONTENT_REASON(mda_is_primary(mda)),
+			       fidtc->raw_metadata_buf))
+			goto_out;
+	} else {
+		/* Write text out, circularly */
+		if (!dev_write(mdac->area.dev, mdac->area.start + mdac->rlocn.offset,
+			       (size_t) (mdac->rlocn.size - new_wrap), MDA_CONTENT_REASON(mda_is_primary(mda)),
+			       fidtc->raw_metadata_buf))
+			goto_out;
 
-	if (new_wrap) {
 		log_debug_metadata("Writing wrapped metadata to %s at " FMTu64 " len " FMTu64 " of " FMTu64,
 				  dev_name(mdac->area.dev), mdac->area.start +
 				  MDA_HEADER_SIZE, new_wrap, mdac->rlocn.size);
diff --git a/lib/format_text/layout.h b/lib/format_text/layout.h
index 1eed664da..bc2559755 100644
--- a/lib/format_text/layout.h
+++ b/lib/format_text/layout.h
@@ -17,6 +17,7 @@
 #define _LVM_TEXT_LAYOUT_H
 
 #include "config.h"
+#include "format-text.h"
 #include "metadata.h"
 #include "lvmcache.h"
 #include "uuid.h"