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dm ioctl: add a new DM_DEV_ARM_POLL ioctl

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This ioctl will record the current global event number in the structure
dm_file, so that next select or poll call will wait until new events
arrived since this ioctl.

The DM_DEV_ARM_POLL ioctl has the same effect as closing and reopening
the handle.

Using the DM_DEV_ARM_POLL ioctl is optional - if the userspace is OK
with closing and reopening the /dev/mapper/control handle after select
or poll, there is no need to re-arm via ioctl.

Usage:
1. open the /dev/mapper/control device
2. send the DM_DEV_ARM_POLL ioctl
3. scan the event numbers of all devices we are interested in and process
   them
4. call select, poll or epoll on the handle (it waits until some new event
   happens since the DM_DEV_ARM_POLL ioctl)
5. go to step 2

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Mikulas Patocka
2017-05-05 11:12:52 -07:00
committed by Mike Snitzer
parent 93e6442c76
commit fc1841e1c1
2 changed files with 38 additions and 22 deletions
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4
include/uapi/linux/dm-ioctl.h
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@@ -240,7 +240,8 @@ enum {
/* Added later */
DM_LIST_VERSIONS_CMD,
DM_TARGET_MSG_CMD,
DM_DEV_SET_GEOMETRY_CMD
DM_DEV_SET_GEOMETRY_CMD,
DM_DEV_ARM_POLL_CMD,
};
#define DM_IOCTL 0xfd
@@ -255,6 +256,7 @@ enum {
#define DM_DEV_SUSPEND _IOWR(DM_IOCTL, DM_DEV_SUSPEND_CMD, struct dm_ioctl)
#define DM_DEV_STATUS _IOWR(DM_IOCTL, DM_DEV_STATUS_CMD, struct dm_ioctl)
#define DM_DEV_WAIT _IOWR(DM_IOCTL, DM_DEV_WAIT_CMD, struct dm_ioctl)
#define DM_DEV_ARM_POLL _IOWR(DM_IOCTL, DM_DEV_ARM_POLL_CMD, struct dm_ioctl)
#define DM_TABLE_LOAD _IOWR(DM_IOCTL, DM_TABLE_LOAD_CMD, struct dm_ioctl)
#define DM_TABLE_CLEAR _IOWR(DM_IOCTL, DM_TABLE_CLEAR_CMD, struct dm_ioctl)