btrfs-progs: fix error checking in load_device_info

load_device_info queries the FS_INFO ioctl and this may fail with EPERM
on older kernels. The check did not verify the ioctl return value and
incorrectly returned EPERM if it was previously stored in errno.

This fixes 'btrfs fi usage' that will print the overall summary for all
users (provided that the FS_INFO ioctl is already unprivileged).

Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 4 insertions, 5 deletions

diff --git a/cmds-fi-usage.c b/cmds-fi-usage.c
index 54b8b1c1..50d63337 100644
--- a/cmds-fi-usage.c
+++ b/cmds-fi-usage.c
@@ -504,7 +504,7 @@ static int cmp_device_info(const void *a, const void *b)
 static int load_device_info(int fd, struct device_info **device_info_ptr,
 			   int *device_info_count)
 {
-	int ret, i, ndevs, e;
+	int ret, i, ndevs;
 	struct btrfs_ioctl_fs_info_args fi_args;
 	struct btrfs_ioctl_dev_info_args dev_info;
 	struct device_info *info;
@@ -513,12 +513,11 @@ static int load_device_info(int fd, struct device_info **device_info_ptr,
 	*device_info_ptr = 0;
 
 	ret = ioctl(fd, BTRFS_IOC_FS_INFO, &fi_args);
-	e = errno;
-	if (e == EPERM)
-		return -e;
 	if (ret < 0) {
+		if (errno == EPERM)
+			return -errno;
 		fprintf(stderr, "ERROR: cannot get filesystem info - %s\n",
-				strerror(e));
+				strerror(errno));
 		return 1;
 	}