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/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
#ifndef _UAPI_LINUX_RINGBUFFER_SYS_H
#define _UAPI_LINUX_RINGBUFFER_SYS_H
#include <uapi/linux/types.h>
/*
* ringbuffer_desc - head and tail pointers for a ringbuffer, mappped to
* userspace:
*/
struct ringbuffer_desc {
/*
* We use u32s because this type is shared between the kernel and
* userspace - ulong/size_t won't work here, we might be 32bit userland
* and 64 bit kernel, and u64 would be preferable (reduced probability
* of ABA) but not all architectures can atomically read/write to a u64;
* we need to avoid torn reads/writes.
*
* head and tail pointers are incremented and stored without masking;
* this is to avoid ABA and differentiate between a full and empty
* buffer - they must be masked with @mask to get an actual offset into
* the data buffer.
*
* All units are in bytes.
*
* Data is emitted at head, consumed from tail.
*/
__u32 head;
__u32 tail;
__u32 size; /* always a power of two */
__u32 mask; /* size - 1 */
/*
* Starting offset of data buffer, from the start of this struct - will
* always be PAGE_SIZE.
*/
__u32 data_offset;
};
#endif /* _UAPI_LINUX_RINGBUFFER_SYS_H */
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