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pager_op_range.md

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zx_pager_op_range

SUMMARY

Perform an operation on a range of a pager owned vmo.

DECLARATION

#include <zircon/syscalls.h>

zx_status_t zx_pager_op_range(zx_handle_t pager,
                              uint32_t op,
                              zx_handle_t pager_vmo,
                              uint64_t offset,
                              uint64_t length,
                              uint64_t data);

DESCRIPTION

Performs a pager operation, specified by op on pager_vmo in the range [offset, offset + length). The pager_vmo must have previously been created from the pager by zx_pager_create_vmo(). offset and length must be page aligned. data is an optional parameter, if the specified op supports one.

Operations that can be performed, i.e. values op can take:

ZX_PAGER_OP_DIRTY - The userspace pager wants to transition pages in the range [offset, offset + length) from clean to dirty. This will unblock any writes that were waiting on ZX_PAGER_VMO_DIRTY page requests for the specified range.

ZX_PAGER_OP_FAIL - The userspace pager failed to fulfill page requests for pager_vmo in the range [offset, offset + length) with command ZX_PAGER_VMO_READ or ZX_PAGER_VMO_DIRTY. data contains the error encountered (a zx_status_t error code sign-extended to a uint64_t value) - permitted values are ZX_ERR_IO, ZX_ERR_IO_DATA_INTEGRITY, ZX_ERR_BAD_STATE and ZX_ERR_NO_SPACE.

This will signal threads that might be waiting on page requests in that range, unblocking them. If the blocked thread was requesting pages through a zx_vmo_read() / zx_vmo_write() or a zx_vmo_op_range() with ZX_VMO_OP_COMMIT, the call will fail and the error status (data) will be returned. If the blocked thread was requesting pages through a VMAR mapping, the thread will take a fatal page fault exception.

ZX_PAGER_OP_WRITEBACK_BEGIN - The userspace pager wants to begin writing back pages in the range [offset, offset + length). This indicates an intent to clean any dirty pages in the specified range once the writeback is completed (signaled with ZX_PAGER_OP_WRITEBACK_END). Refer to the sample code below for suggested usage.

ZX_PAGER_OP_WRITEBACK_END - The userspace pager is done writing back pages in the range [offset, offset + length). This indicates that any dirty pages in the specified range that were previously signaled with ZX_PAGER_OP_WRITEBACK_BEGIN can be marked clean. Refer to the sample code below for suggested usage.

Sample code (modulo error handling) to discover and clean any dirty pages might look something like this.

  zx_vmo_dirty_range_t ranges[kMaxRanges];
  uint64_t num_ranges;

  zx_status_t st =
      zx_pager_query_dirty_ranges(pager, vmo, 0, vmo_size, &ranges[0],
                                  kMaxRanges * sizeof(zx_vmo_dirty_range_t), &num_ranges, nullptr);

  for (uint64_t i = 0; i < num_ranges; i++) {
    uint64_t start = ranges[i].offset;
    uint64_t len = ranges[i].length;
    st = zx_pager_op_range(pager, ZX_PAGER_OP_WRITEBACK_BEGIN, vmo, start, len, 0);
    WritebackToDisk(vmo, start, len);
    st = zx_pager_op_range(pager, ZX_PAGER_OP_WRITEBACK_END, vmo, start, len, 0);
  }

RIGHTS

pager must be of type ZX_OBJ_TYPE_PAGER.

pager_vmo must be of type ZX_OBJ_TYPE_VMO.

RETURN VALUE

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

ERRORS

ZX_ERR_BAD_HANDLE pager or pager_vmo is not a valid handle.

ZX_ERR_WRONG_TYPE pager is not a pager handle, or pager_vmo is not a vmo handle.

ZX_ERR_INVALID_ARGS pager_vmo is not a vmo created from pager, or offset or length is not page aligned, or op is ZX_PAGER_OP_FAIL and data is not one of ZX_ERR_IO, ZX_ERR_IO_DATA_INTEGRITY or ZX_ERR_BAD_STATE.

ZX_ERR_OUT_OF_RANGE The specified range in pager_vmo is invalid.

ZX_ERR_NOT_SUPPORTED op is not supported on the specified range in pager_vmo.

SEE ALSO