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zx_pager_create_vmo

Summary

Create a pager owned vmo.

Declaration

#include <zircon/syscalls.h>

zx_status_t zx_pager_create_vmo(zx_handle_t pager,
                                uint32_t options,
                                zx_handle_t port,
                                uint64_t key,
                                uint64_t size,
                                zx_handle_t* out);

Description

Creates a VMO owned by a pager object. size will be rounded up to the next page size boundary, and options must be zero or any combination of the following flags:

ZX_VMO_RESIZABLE - if the VMO can be resized.

ZX_VMO_TRAP_DIRTY - if writes to clean pages in the VMO should be trapped by the kernel and forwarded to the pager service for acknowledgement before proceeding with the write.

On success, the returned vmo has the same rights as a vmo created with zx_vmo_create(), as well as having the same behavior with respect to ZX_VMO_ZERO_CHILDREN. Syscalls that operate on VMOs require an explicit flag to allow blocking IPC to the userspace pager service; beyond this, whether or not a VMO is owned by a pager does not affect the semantics of syscalls.

TODO(stevend): Update differences after updates to cloning and decommit

Page requests will be delivered to port when certain conditions are met. Those packets will have type set to ZX_PKT_TYPE_PAGE_REQUEST and key set to the value provided to zx_pager_create_vmo(). The packet's union is of type zx_packet_page_request_t:

typedef struct zx_packet_page_request {
    uint16_t command;
    uint16_t flags;
    uint32_t reserved0;
    uint64_t offset;
    uint64_t length;
    uint64_t reserved1;
} zx_packet_page_request_t;

offset and length are always page-aligned. The value of any bits in flags for which flags are not defined is unspecified - currently no flags are defined. The trigger and meaning of the packet depends on command, which can take one of the following values:

ZX_PAGER_VMO_READ: Sent when an application accesses a non-resident page in a pager's VMO. The pager service should populate the range [offset, offset + length) in the registered vmo with zx_pager_supply_pages(). Supplying pages is an implicit positive acknowledgement of the request.

ZX_PAGER_VMO_DIRTY: Sent when an application writes to a resident clean page in a pager's VMO created with the ZX_VMO_TRAP_DIRTY flag. The pager service should acknowledge that the range [offset, offset + length) can be dirtied, allowing the write to proceed, with zx_pager_op_range() ZX_PAGER_OP_DIRTY.

ZX_PAGER_VMO_COMPLETE: Sent when no more pager requests will be sent for the corresponding VMO, either because of zx_pager_detach_vmo() or because no references to the VMO remain.

If pager is closed, then no more packets will be delivered to port (including no ZX_PAGER_VMO_COMPLETE message). Furthermore, all future accesses will behave as if zx_pager_detach_vmo() had been called.

Rights

pager must be of type ZX_OBJ_TYPE_PAGER.

port must be of type ZX_OBJ_TYPE_PORT and have ZX_RIGHT_WRITE.

Return value

zx_pager_create_vmo() returns ZX_OK on success, or one of the following error codes on failure.

Errors

ZX_ERR_INVALID_ARGS out is an invalid pointer or NULL, or options is any value other than 0 or ZX_VMO_RESIZABLE.

ZX_ERR_BAD_HANDLE pager or port is not a valid handle.

ZX_ERR_ACCESS_DENIED port does not have ZX_RIGHT_WRITE.

ZX_ERR_WRONG_TYPE pager is not a pager handle or port is not a port handle.

ZX_ERR_OUT_OF_RANGE The requested size is larger than the maximum vmo size.

ZX_ERR_NO_MEMORY Failure due to lack of memory.

See also