SCTX-1536: Option to use the back-up footer instead of the primary one.

Signed-off-by: Thanos Makatos <[email protected]> Reviewed-by: Keith Petley <[email protected]> GitHub: closes #55 on xapi-project/blktap
xapi-project · Oct 4, 2013 · ec6e15f · ec6e15f
1 parent f8b4c0d
commit ec6e15f
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Showing 5 changed files with 31 additions and 17 deletions.
diff --git a/drivers/td.c b/drivers/td.c
@@ -399,8 +399,9 @@ td_query(int type, int argc, char *argv[])
 {
 	char *name;
 	int c, size = 0, parent = 0, fields = 0, depth = 0, err = 0;
+	int flags = VHD_OPEN_RDONLY;
 
-	while ((c = getopt(argc, argv, "hvpfd")) != -1) {
+	while ((c = getopt(argc, argv, "hvpfdb")) != -1) {
 		switch(c) {
 		case 'v':
 			size = 1;
@@ -417,6 +418,9 @@ td_query(int type, int argc, char *argv[])
 		case 'h':
 			err = 0;
 			goto usage;
+		case 'b':
+			flags |= VHD_OPEN_USE_BKP_FOOTER;
+			break;
 		default:
 			err = EINVAL;
 			goto usage;
@@ -438,7 +442,7 @@ td_query(int type, int argc, char *argv[])
 	if (type == TD_TYPE_VHD) {
 		vhd_context_t vhd;
 
-		err = vhd_open(&vhd, name, VHD_OPEN_RDONLY);
+		err = vhd_open(&vhd, name, flags);
 		if (err) {
 			printf("failed opening %s: %d\n", name, err);
 			return err;
@@ -531,7 +535,8 @@ td_query(int type, int argc, char *argv[])
 
  usage:
 	fprintf(stderr, "usage: td-util query %s [-h help] [-v virtsize] "
-		"[-p parent] [-f fields]  <FILENAME>\n", td_disk_types[type]);
+		"[-p parent] [-f fields] [-b don't trust the footer, use the back-up "
+		"one instead] <FILENAME>\n", td_disk_types[type]);
 	return err;
 }
 

diff --git a/include/libvhd.h b/include/libvhd.h
@@ -22,6 +22,7 @@
 #include <endian.h>
 #include <byteswap.h>
 #include <uuid/uuid.h>
+#include <stdbool.h>
 
 #include "vhd.h"
 #include "list.h"
@@ -63,6 +64,7 @@
 #define VHD_OPEN_IGNORE_DISABLED   0x00010
 #define VHD_OPEN_CACHED            0x00020
 #define VHD_OPEN_IO_WRITE_SPARSE   0x00040
+#define VHD_OPEN_USE_BKP_FOOTER    0x00080
 
 #define VHD_FLAG_CREAT_FILE_SIZE_FIXED   0x00001
 #define VHD_FLAG_CREAT_PARENT_RAW        0x00002
@@ -312,7 +314,7 @@ int vhd_change_parent(vhd_context_t *, char *parent_path, int raw);
 int vhd_macx_encode_location(char *name, char **out, int *outlen);
 int vhd_w2u_encode_location(char *name, char **out, int *outlen);
 
-int vhd_read_footer(vhd_context_t *, vhd_footer_t *);
+int vhd_read_footer(vhd_context_t *, vhd_footer_t *, bool use_bkp_footer);
 int vhd_read_footer_at(vhd_context_t *, vhd_footer_t *, off64_t);
 int vhd_read_footer_strict(vhd_context_t *, vhd_footer_t *);
 int vhd_read_header(vhd_context_t *, vhd_header_t *);

diff --git a/vhd/lib/libvhd.c b/vhd/lib/libvhd.c
@@ -769,7 +769,7 @@ vhd_get_footer(vhd_context_t *ctx)
 	if (!vhd_validate_footer(&ctx->footer))
 		return 0;
 
-	return vhd_read_footer(ctx, &ctx->footer);
+	return vhd_read_footer(ctx, &ctx->footer, false);
 }
 
 int
@@ -935,7 +935,7 @@ vhd_read_footer_at(vhd_context_t *ctx, vhd_footer_t *footer, off64_t off)
 }
 
 int
-vhd_read_footer(vhd_context_t *ctx, vhd_footer_t *footer)
+vhd_read_footer(vhd_context_t *ctx, vhd_footer_t *footer, bool use_bkp_footer)
 {
 	int err;
 	off64_t off;
@@ -948,13 +948,15 @@ vhd_read_footer(vhd_context_t *ctx, vhd_footer_t *footer)
 	if (off == (off64_t)-1)
 		return -errno;
 
-	err = vhd_read_footer_at(ctx, footer, off - 512);
-	if (err != -EINVAL)
-		return err;
+	if (!use_bkp_footer) {
+		err = vhd_read_footer_at(ctx, footer, off - 512);
+		if (err != -EINVAL)
+			return err;
 
-	err = vhd_read_short_footer(ctx, footer);
-	if (err != -EINVAL)
-		return err;
+		err = vhd_read_short_footer(ctx, footer);
+		if (err != -EINVAL)
+			return err;
+	}
 
 	/* 
 	 * Disable the enforcement of VHD_OPEN_STRICT until we figure out how 
@@ -2523,7 +2525,8 @@ vhd_open(vhd_context_t *ctx, const char *file, int flags)
 		return 0;
 	}
 
-	err = vhd_read_footer(ctx, &ctx->footer);
+	err = vhd_read_footer(ctx, &ctx->footer,
+			(flags & VHD_OPEN_USE_BKP_FOOTER) == VHD_OPEN_USE_BKP_FOOTER);
 	if (err)
 		goto fail;
 

diff --git a/vhd/lib/vhd-util-read.c b/vhd/lib/vhd-util-read.c
@@ -309,7 +309,7 @@ vhd_dump_headers(const char *name, int hex)
 
 	vhd.file = strdup(name);
 
-	vhd_read_footer(&vhd, &vhd.footer);
+	vhd_read_footer(&vhd, &vhd.footer, false);
 	vhd_read_header(&vhd, &vhd.header);
 
 	vhd_print_footer(&vhd.footer, hex);

diff --git a/vhd/lib/vhd-util-repair.c b/vhd/lib/vhd-util-repair.c
@@ -33,18 +33,22 @@ vhd_util_repair(int argc, char **argv)
 	char *name;
 	int err, c;
 	vhd_context_t vhd;
+	int flags = VHD_OPEN_RDWR;
 
 	name = NULL;
 
 	if (!argc || !argv)
 		goto usage;
 
 	optind = 0;
-	while ((c = getopt(argc, argv, "n:h")) != -1) {
+	while ((c = getopt(argc, argv, "n:bh")) != -1) {
 		switch (c) {
 		case 'n':
 			name = optarg;
 			break;
+		case 'b':
+			flags |= VHD_OPEN_USE_BKP_FOOTER;
+			break;
 		case 'h':
 		default:
 			goto usage;
@@ -54,7 +58,7 @@ vhd_util_repair(int argc, char **argv)
 	if (!name || optind != argc)
 		goto usage;
 
-	err = vhd_open(&vhd, name, VHD_OPEN_RDWR);
+	err = vhd_open(&vhd, name, flags);
 	if (err) {
 		printf("error opening %s: %d\n", name, err);
 		return err;
@@ -68,6 +72,6 @@ vhd_util_repair(int argc, char **argv)
 	return err;
 
 usage:
-	printf("options: <-n name> [-h help]\n");
+	printf("options: <-n name> <-b use the back-up footer> [-h help]\n");
 	return -EINVAL;
 }