This allows userspace to completely setup a loop device with a single
ioctl, removing the in-between state where the device can be partially
configured - eg the loop device has a backing file associated with it,
but is reading from the wrong offset.
Besides removing the intermediate state, another big benefit of this
ioctl is that LOOP_SET_STATUS can be slow; the main reason for this
slowness is that LOOP_SET_STATUS(64) calls blk_mq_freeze_queue() to
freeze the associated queue; this requires waiting for RCU
synchronization, which I've measured can take about 15-20ms on this
device on average.
Here's setting up ~70 regular loop devices with an offset on an x86
Android device, using LOOP_SET_FD and LOOP_SET_STATUS:
vsoc_x86:/system/apex # time for i in `seq 30 100`;
do losetup -r -o 4096 /dev/block/loop$i com.android.adbd.apex; done
0m03.40s real 0m00.02s user 0m00.03s system
Here's configuring ~70 devices in the same way, but using a modified
losetup that uses the new LOOP_SET_FD_AND_STATUS ioctl:
vsoc_x86:/system/apex # time for i in `seq 30 100`;
do losetup -r -o 4096 /dev/block/loop$i com.android.adbd.apex; done
0m01.94s real 0m00.01s user 0m00.01s system
Signed-off-by: Martijn Coenen <maco@xxxxxxxxxxx>
---
drivers/block/loop.c | 47 ++++++++++++++++++++++++++++++---------
include/uapi/linux/loop.h | 6 +++++
2 files changed, 42 insertions(+), 11 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 6e656390b285..e1dbd70d6d6e 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1065,8 +1065,9 @@ loop_set_from_status(struct loop_device *lo, const struct loop_info64 *info)
return 0;
}
-static int loop_set_fd(struct loop_device *lo, fmode_t mode,
- struct block_device *bdev, unsigned int arg)
+static int loop_set_fd_and_status(struct loop_device *lo, fmode_t mode,
+ struct block_device *bdev, unsigned int fd,
+ const struct loop_info64 *info)
{
struct file *file;
struct inode *inode;
@@ -1081,7 +1082,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
__module_get(THIS_MODULE);
error = -EBADF;
- file = fget(arg);
+ file = fget(fd);
if (!file)
goto out;
@@ -1090,7 +1091,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
* here to avoid changing device under exclusive owner.
*/
if (!(mode & FMODE_EXCL)) {
- claimed_bdev = bd_start_claiming(bdev, loop_set_fd);
+ claimed_bdev = bd_start_claiming(bdev, loop_set_fd_and_status);
if (IS_ERR(claimed_bdev)) {
error = PTR_ERR(claimed_bdev);
goto out_putf;
@@ -1117,9 +1118,24 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
lo_flags |= LO_FLAGS_READ_ONLY;
error = -EFBIG;
- size = get_loop_size(lo, file);
+ if (info)
+ size = get_size(info->lo_offset, info->lo_sizelimit,
+ file);
+ else
+ size = get_loop_size(lo, file);
if ((loff_t)(sector_t)size != size)
goto out_unlock;
+
+ if (info) {
+ error = loop_set_from_status(lo, info);
+ if (error)
+ goto out_unlock;
+ } else {
+ lo->transfer = NULL;
+ lo->ioctl = NULL;
+ lo->lo_sizelimit = 0;
+ lo->lo_offset = 0;
+ }
error = loop_prepare_queue(lo);
if (error)
goto out_unlock;
@@ -1132,9 +1148,6 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
lo->lo_device = bdev;
lo->lo_flags = lo_flags;
lo->lo_backing_file = file;
- lo->transfer = NULL;
- lo->ioctl = NULL;
- lo->lo_sizelimit = 0;
lo->old_gfp_mask = mapping_gfp_mask(mapping);
mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
@@ -1172,14 +1185,14 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
if (partscan)
loop_reread_partitions(lo, bdev);
if (claimed_bdev)
- bd_abort_claiming(bdev, claimed_bdev, loop_set_fd);
+ bd_abort_claiming(bdev, claimed_bdev, loop_set_fd_and_status);
return 0;
out_unlock:
mutex_unlock(&loop_ctl_mutex);
out_bdev:
if (claimed_bdev)
- bd_abort_claiming(bdev, claimed_bdev, loop_set_fd);
+ bd_abort_claiming(bdev, claimed_bdev, loop_set_fd_and_status);
out_putf:
fput(file);
out:
@@ -1653,7 +1666,18 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
switch (cmd) {
case LOOP_SET_FD:
- return loop_set_fd(lo, mode, bdev, arg);
+ return loop_set_fd_and_status(lo, mode, bdev, arg, NULL);
+ case LOOP_SET_FD_AND_STATUS: {
+ struct loop_fd_and_status fds;
+
+ if (copy_from_user(&fds,
+ (struct loop_fd_and_status __user *) arg,
+ sizeof(fds)))
+ return -EFAULT;
+
+ return loop_set_fd_and_status(lo, mode, bdev, fds.fd,
+ &fds.info);
+ }
case LOOP_CHANGE_FD:
return loop_change_fd(lo, bdev, arg);
case LOOP_CLR_FD:
@@ -1827,6 +1851,7 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
case LOOP_CLR_FD:
case LOOP_GET_STATUS64:
case LOOP_SET_STATUS64:
+ case LOOP_SET_FD_AND_STATUS:
arg = (unsigned long) compat_ptr(arg);
/* fall through */
case LOOP_SET_FD:
diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h
index 080a8df134ef..fcc9a693b588 100644
--- a/include/uapi/linux/loop.h
+++ b/include/uapi/linux/loop.h
@@ -60,6 +60,11 @@ struct loop_info64 {
__u64 lo_init[2];
};
+struct loop_fd_and_status {
+ struct loop_info64 info;
+ __u32 fd;
+};
+
/*
* Loop filter types
*/
@@ -90,6 +95,7 @@ struct loop_info64 {
#define LOOP_SET_CAPACITY 0x4C07
#define LOOP_SET_DIRECT_IO 0x4C08
#define LOOP_SET_BLOCK_SIZE 0x4C09
+#define LOOP_SET_FD_AND_STATUS 0x4C0A
/* /dev/loop-control interface */
#define LOOP_CTL_ADD 0x4C80
--
2.26.1.301.g55bc3eb7cb9-goog
