table of contents
|SF_BUF(9)||Kernel Developer's Manual||SF_BUF(9)|
NAME¶sf_buf — manage temporary kernel address space mapping for memory pages
SYNOPSIS¶#include <sys/sf_buf.h> struct sf_buf *
sf_buf_alloc(struct vm_page *m, int flags); void
sf_buf_free(struct sf_buf *sf); vm_offset_t
sf_buf_kva(struct sf_buf *sf); struct vm_page *
sf_buf_page(struct sf_buf *sf);
DESCRIPTION¶The sf_buf interface, historically the sendfile(2) buffer interface, allows kernel subsystems to manage temporary kernel address space mappings for physical memory pages. On systems with a direct memory map region (allowing all physical pages to be visible in the kernel address space at all times), the struct sf_buf will point to an address in the direct map region; on systems without a direct memory map region, the struct sf_buf will manage a temporary kernel address space mapping valid for the lifetime of the struct sf_buf. Call sf_buf_alloc() to allocate a struct sf_buf for a physical memory page. sf_buf_alloc() is not responsible for arranging for the page to be present in physical memory; the caller should already have arranged for the page to be wired, i.e., by calling vm_page_wire(9). Several flags may be passed to sf_buf_alloc():
- Cause sf_buf_alloc() to abort and return
NULLif a signal is received waiting for a struct sf_buf to become available.
- Cause sf_buf_alloc() to return
NULLrather than sleeping if a struct sf_buf is not immediately available.
- Cause sf_buf_alloc() to only arrange that the temporary mapping be valid on the current CPU, avoiding unnecessary TLB shootdowns for mappings that will only be accessed on a single CPU at a time. The caller must ensure that accesses to the virtual address occur only on the CPU from which sf_buf_alloc() was invoked, perhaps by using sched_pin().
SEE ALSO¶sendfile(2), vm_page_wire(9)
AUTHORS¶The struct sf_buf API was designed and implemented by Alan L. Cox. This manual page was written by Robert N. M. Watson.
|January 28, 2007||Debian|