samsung-ipc: utils.c: file_data_{read,write}: report open error

Mounting the EFS on your local computer can result in user id
and permissions mismatch because the /etc/fstab doesn't always
match the user ids used by Android.

For instance here's the GT-N7000 EFS on my laptop:
    $ ls -l [...]/nv_data.bin
    -rwx------ 1 1001 1001 2097152  1 janv.  2000 [...]/nv_data.bin

When using nv_data-md5 on it we have:
    $ ./tools/nv_data-md5 [...]/nv_data.bin
    [ipc] file_data_read: Error: fd: -1
    [ipc] ipc_nv_data_md5_calculate failed: data is NULL
    Calculating nv_data backup md5 failed

The error was too cryptic, and I ended up having to dig into the source
code to understand what was going on.

With this patch we now have an error message that is easier to understand:
    $ ./tools/nv_data-md5 [...]/nv_data.bin
    [ipc] file_data_read open failed with error 13: Permission denied
    [ipc] ipc_nv_data_md5_calculate failed: data is NULL
    Calculating nv_data backup md5 failed

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/samsung-ipc/utils.c b/samsung-ipc/utils.c
index 85f06cf..0e6bc2f 100644
--- a/samsung-ipc/utils.c
+++ b/samsung-ipc/utils.c
@@ -18,6 +18,7 @@
  */
 
 #include <ctype.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -70,7 +71,9 @@ void *file_data_read(struct ipc_client *client, const char *path, size_t size,
 
 	fd = open(path, O_RDONLY);
 	if (fd < 0) {
-		ipc_client_log(client, "%s: Error: fd: %d ", __func__, fd);
+		rc = errno;
+		ipc_client_log(client, "%s open failed with error %d: %s", __func__, rc,
+			       strerror(rc));
 		goto error;
 	}
 
@@ -147,8 +150,9 @@ int file_data_write(struct ipc_client *client, const char *path,
 
 	fd = open(path, O_WRONLY | O_CREAT, 0644);
 	if (fd < 0) {
-		ipc_client_log(client, "%s: open failed with error %d",
-			       __func__, fd);
+		rc = errno;
+		ipc_client_log(client, "%s open failed with error %d: %s",
+			       __func__, rc, strerror(rc));
 		goto error;
 	}