Let cgpt open devices in read-only mode when possible.

BUG=chromium-os:12430
TEST=manual

Running "make; make runtests" in src/platform/vboot_refererence will test
this change. Tests for use on a Chromebook are described in the bug report,
but will require a USB or SD card that has a physical write-protect switch.

Change-Id: I16a67bad3b59bec0981f4064f51fb1a29da65a90
Reviewed-on: https://gerrit.chromium.org/gerrit/21474
Tested-by: Bill Richardson <wfrichar@chromium.org>
Commit-Ready: Bill Richardson <wfrichar@chromium.org>
Reviewed-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: Che-Liang Chiou <clchiou@chromium.org>

9 files changed, 24 insertions, 16 deletions

diff --git a/cgpt/cgpt.h b/cgpt/cgpt.h
index 1c809161..6851ded7 100644
--- a/cgpt/cgpt.h
+++ b/cgpt/cgpt.h
@@ -10,6 +10,7 @@
 #endif
 
 #define _FILE_OFFSET_BITS 64
+#include <fcntl.h>
 #include <features.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -61,7 +62,8 @@ struct drive {
 };
 
 
-int DriveOpen(const char *drive_path, struct drive *drive);
+/* mode should be O_RDONLY or O_RDWR */
+int DriveOpen(const char *drive_path, struct drive *drive, int mode);
 int DriveClose(struct drive *drive, int update_as_needed);
 int CheckValid(const struct drive *drive);
 
diff --git a/cgpt/cgpt_add.c b/cgpt/cgpt_add.c
index e3e1a483..a3d0fb99 100644
--- a/cgpt/cgpt_add.c
+++ b/cgpt/cgpt_add.c
@@ -39,7 +39,7 @@ int cgpt_set_attributes(CgptAddParams *params) {
   if (params == NULL)
     return CGPT_FAILED;
 
-  if (CGPT_OK != DriveOpen(params->drive_name, &drive))
+  if (CGPT_OK != DriveOpen(params->drive_name, &drive, O_RDWR))
     return CGPT_FAILED;
 
   if (GPT_SUCCESS != (gpt_retval = GptSanityCheck(&drive.gpt))) {
@@ -101,7 +101,7 @@ int cgpt_get_partition_details(CgptAddParams *params) {
   if (params == NULL)
     return result;
 
-  if (CGPT_OK != DriveOpen(params->drive_name, &drive)) {
+  if (CGPT_OK != DriveOpen(params->drive_name, &drive, O_RDWR)) {
     Error("Unable to open drive: %s\n", params->drive_name);
     return result;
   }
@@ -183,7 +183,7 @@ int cgpt_add(CgptAddParams *params) {
   if (params == NULL)
     return CGPT_FAILED;
 
-  if (CGPT_OK != DriveOpen(params->drive_name, &drive))
+  if (CGPT_OK != DriveOpen(params->drive_name, &drive, O_RDWR))
     return CGPT_FAILED;
 
   if (GPT_SUCCESS != (gpt_retval = GptSanityCheck(&drive.gpt))) {
diff --git a/cgpt/cgpt_boot.c b/cgpt/cgpt_boot.c
index 33c5471c..f8e712d6 100644
--- a/cgpt/cgpt_boot.c
+++ b/cgpt/cgpt_boot.c
@@ -21,7 +21,7 @@ int cgpt_get_boot_partition_number(CgptBootParams *params) {
   if (params == NULL)
     return CGPT_FAILED;
 
-  if (CGPT_OK != DriveOpen(params->drive_name, &drive))
+  if (CGPT_OK != DriveOpen(params->drive_name, &drive, O_RDONLY))
     return CGPT_FAILED;
 
   if (GPT_SUCCESS != (gpt_retval = GptSanityCheck(&drive.gpt))) {
@@ -65,12 +65,17 @@ int cgpt_boot(CgptBootParams *params) {
   struct drive drive;
   int retval = 1;
   int gpt_retval= 0;
+  int mode = O_RDONLY;
 
   if (params == NULL)
     return CGPT_FAILED;
 
-  if (CGPT_OK != DriveOpen(params->drive_name, &drive))
+  if (params->create_pmbr || params->partition || params->bootfile)
+    mode = O_RDWR;
+
+  if (CGPT_OK != DriveOpen(params->drive_name, &drive, mode)) {
     return CGPT_FAILED;
+  }
 
   if (CGPT_OK != ReadPMBR(&drive)) {
     Error("Unable to read PMBR\n");
@@ -135,8 +140,8 @@ int cgpt_boot(CgptBootParams *params) {
   GuidToStr(&drive.pmbr.boot_guid, buf, sizeof(buf));
   printf("%s\n", buf);
 
-  // Write it all out
-  if (CGPT_OK == WritePMBR(&drive))
+  // Write it all out, if needed.
+  if (mode == O_RDONLY || CGPT_OK == WritePMBR(&drive))
     retval = 0;
 
 done:
diff --git a/cgpt/cgpt_common.c b/cgpt/cgpt_common.c
index a5a509b1..d69eb670 100644
--- a/cgpt/cgpt_common.c
+++ b/cgpt/cgpt_common.c
@@ -153,10 +153,11 @@ static int Save(const int fd, const uint8_t *buf,
 
 
 // Opens a block device or file, loads raw GPT data from it.
+// mode should be O_RDONLY or O_RDWR
 //
 // Returns CGPT_FAILED if any error happens.
 // Returns CGPT_OK if success and information are stored in 'drive'. */
-int DriveOpen(const char *drive_path, struct drive *drive) {
+int DriveOpen(const char *drive_path, struct drive *drive, int mode) {
   struct stat stat;
 
   require(drive_path);
@@ -165,7 +166,7 @@ int DriveOpen(const char *drive_path, struct drive *drive) {
   // Clear struct for proper error handling.
   memset(drive, 0, sizeof(struct drive));
 
-  drive->fd = open(drive_path, O_RDWR | O_LARGEFILE | O_NOFOLLOW);
+  drive->fd = open(drive_path, mode | O_LARGEFILE | O_NOFOLLOW);
   if (drive->fd == -1) {
     Error("Can't open %s: %s\n", drive_path, strerror(errno));
     return CGPT_FAILED;
diff --git a/cgpt/cgpt_create.c b/cgpt/cgpt_create.c
index dc25d8fa..8c899d19 100644
--- a/cgpt/cgpt_create.c
+++ b/cgpt/cgpt_create.c
@@ -15,7 +15,7 @@ int cgpt_create(CgptCreateParams *params) {
   if (params == NULL)
     return CGPT_FAILED;
 
-  if (CGPT_OK != DriveOpen(params->drive_name, &drive))
+  if (CGPT_OK != DriveOpen(params->drive_name, &drive, O_RDWR))
     return CGPT_FAILED;
 
   // Erase the data
diff --git a/cgpt/cgpt_find.c b/cgpt/cgpt_find.c
index 20070209..345c8310 100644
--- a/cgpt/cgpt_find.c
+++ b/cgpt/cgpt_find.c
@@ -94,7 +94,7 @@ static int do_search(CgptFindParams *params, char *fileName) {
   GptEntry *entry;
   char partlabel[GPT_PARTNAME_LEN];
 
-  if (CGPT_OK != DriveOpen(fileName, &drive))
+  if (CGPT_OK != DriveOpen(fileName, &drive, O_RDONLY))
     return 0;
 
   if (GPT_SUCCESS != GptSanityCheck(&drive.gpt)) {
diff --git a/cgpt/cgpt_prioritize.c b/cgpt/cgpt_prioritize.c
index 107c00a9..2b3feb06 100644
--- a/cgpt/cgpt_prioritize.c
+++ b/cgpt/cgpt_prioritize.c
@@ -108,7 +108,7 @@ int cgpt_prioritize(CgptPrioritizeParams *params) {
   if (params == NULL)
     return CGPT_FAILED;
 
-  if (CGPT_OK != DriveOpen(params->drive_name, &drive))
+  if (CGPT_OK != DriveOpen(params->drive_name, &drive, O_RDWR))
     return CGPT_FAILED;
 
   if (GPT_SUCCESS != (gpt_retval = GptSanityCheck(&drive.gpt))) {
diff --git a/cgpt/cgpt_repair.c b/cgpt/cgpt_repair.c
index 96d3fb1c..97beef84 100644
--- a/cgpt/cgpt_repair.c
+++ b/cgpt/cgpt_repair.c
@@ -15,7 +15,7 @@ int cgpt_repair(CgptRepairParams *params) {
   if (params == NULL)
     return CGPT_FAILED;
 
-  if (CGPT_OK != DriveOpen(params->drive_name, &drive))
+  if (CGPT_OK != DriveOpen(params->drive_name, &drive, O_RDWR))
     return CGPT_FAILED;
 
   int gpt_retval = GptSanityCheck(&drive.gpt);
diff --git a/cgpt/cgpt_show.c b/cgpt/cgpt_show.c
index d4170b1c..f0022a9d 100644
--- a/cgpt/cgpt_show.c
+++ b/cgpt/cgpt_show.c
@@ -186,7 +186,7 @@ int cgpt_get_num_non_empty_partitions(CgptShowParams *params) {
   if (params == NULL)
     return CGPT_FAILED;
 
-  if (CGPT_OK != DriveOpen(params->drive_name, &drive))
+  if (CGPT_OK != DriveOpen(params->drive_name, &drive, O_RDONLY))
     return CGPT_FAILED;
 
   if (GPT_SUCCESS != (gpt_retval = GptSanityCheck(&drive.gpt))) {
@@ -221,7 +221,7 @@ int cgpt_show(CgptShowParams *params) {
   if (params == NULL)
     return CGPT_FAILED;
 
-  if (CGPT_OK != DriveOpen(params->drive_name, &drive))
+  if (CGPT_OK != DriveOpen(params->drive_name, &drive, O_RDONLY))
     return CGPT_FAILED;
 
   if (GPT_SUCCESS != (gpt_retval = GptSanityCheck(&drive.gpt))) {