[PATCH v5 10/11] loop: Clean up LOOP_SET_STATUS lo_flags handling

Martijn Coenen
2020-05-13T13:39:27Z

LOOP_SET_STATUS(64) will actually allow some lo_flags to be modified; in
particular, LO_FLAGS_AUTOCLEAR can be set and cleared, whereas
LO_FLAGS_PARTSCAN can be set to request a partition scan. Make this
explicit by updating the UAPI to include the flags that can be
set/cleared using this ioctl.

The implementation can then blindly take over the passed in flags,
and use the previous flags for those flags that can't be set / cleared
using LOOP_SET_STATUS.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martijn Coenen <maco@android.com>
---
drivers/block/loop.c | 19 +++++++++++++------
include/uapi/linux/loop.h | 10 ++++++++--
2 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 31f10da4945e..13518ba191f5 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1036,9 +1036,7 @@ loop_set_status_from_info(struct loop_device *lo,
lo->transfer = xfer->transfer;
lo->ioctl = xfer->ioctl;

- if ((lo->lo_flags & LO_FLAGS_AUTOCLEAR) !=
- (info->lo_flags & LO_FLAGS_AUTOCLEAR))
- lo->lo_flags ^= LO_FLAGS_AUTOCLEAR;
+ lo->lo_flags = info->lo_flags;

lo->lo_encrypt_key_size = info->lo_encrypt_key_size;
lo->lo_init[0] = info->lo_init[0];
@@ -1323,6 +1321,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
int err;
struct block_device *bdev;
kuid_t uid = current_uid();
+ int prev_lo_flags;
bool partscan = false;
bool size_changed = false;

@@ -1359,10 +1358,19 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
goto out_unfreeze;
}

+ prev_lo_flags = lo->lo_flags;
+
err = loop_set_status_from_info(lo, info);
if (err)
goto out_unfreeze;

+ /* Mask out flags that can't be set using LOOP_SET_STATUS. */
+ lo->lo_flags &= ~LOOP_SET_STATUS_SETTABLE_FLAGS;
+ /* For those flags, use the previous values instead */
+ lo->lo_flags |= prev_lo_flags & ~LOOP_SET_STATUS_SETTABLE_FLAGS;
+ /* For flags that can't be cleared, use previous values too */
+ lo->lo_flags |= prev_lo_flags & ~LOOP_SET_STATUS_CLEARABLE_FLAGS;
+
if (size_changed) {
loff_t new_size = get_size(lo->lo_offset, lo->lo_sizelimit,
lo->lo_backing_file);
@@ -1377,9 +1385,8 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
out_unfreeze:
blk_mq_unfreeze_queue(lo->lo_queue);

- if (!err && (info->lo_flags & LO_FLAGS_PARTSCAN) &&
- !(lo->lo_flags & LO_FLAGS_PARTSCAN)) {
- lo->lo_flags |= LO_FLAGS_PARTSCAN;
+ if (!err && (lo->lo_flags & LO_FLAGS_PARTSCAN) &&
+ !(prev_lo_flags & LO_FLAGS_PARTSCAN)) {
lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
bdev = lo->lo_device;
partscan = true;
diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h
index 080a8df134ef..6b32fee80ce0 100644
--- a/include/uapi/linux/loop.h
+++ b/include/uapi/linux/loop.h
@@ -25,6 +25,12 @@ enum {
LO_FLAGS_DIRECT_IO = 16,
};

+/* LO_FLAGS that can be set using LOOP_SET_STATUS(64) */
+#define LOOP_SET_STATUS_SETTABLE_FLAGS (LO_FLAGS_AUTOCLEAR | LO_FLAGS_PARTSCAN)
+
+/* LO_FLAGS that can be cleared using LOOP_SET_STATUS(64) */
+#define LOOP_SET_STATUS_CLEARABLE_FLAGS (LO_FLAGS_AUTOCLEAR)
+
#include <asm/posix_types.h> /* for __kernel_old_dev_t */
#include <linux/types.h> /* for __u64 */

@@ -37,7 +43,7 @@ struct loop_info {
int lo_offset;
int lo_encrypt_type;
int lo_encrypt_key_size; /* ioctl w/o */
- int lo_flags; /* ioctl r/o */
+ int lo_flags;
char lo_name[LO_NAME_SIZE];
unsigned char lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */
unsigned long lo_init[2];
@@ -53,7 +59,7 @@ struct loop_info64 {
__u32 lo_number; /* ioctl r/o */
__u32 lo_encrypt_type;
__u32 lo_encrypt_key_size; /* ioctl w/o */
- __u32 lo_flags; /* ioctl r/o */
+ __u32 lo_flags;
__u8 lo_file_name[LO_NAME_SIZE];
__u8 lo_crypt_name[LO_NAME_SIZE];
__u8 lo_encrypt_key[LO_KEY_SIZE]; /* ioctl w/o */
--
2.26.2.645.ge9eca65c58-goog