SF_BUF_FREE(9FREEBSD) - man page online | system kernel interfaces

Manage temporary kernel address space mapping for memory pages.

January 28, 2007
SF_BUF(9)                         BSD Kernel Developer's Manual                         SF_BUF(9)


sf_buf — manage temporary kernel address space mapping for memory pages


#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);


The sf_buf interface, historically the sendfile(2) buffer interface, allows kernel subsys‐ tems to manage temporary kernel address space mappings for physical memory pages. On sys‐ tems with a direct memory map region (allowing all physical pages to be visible in the ker‐ nel 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(): SFB_CATCH Cause sf_buf_alloc() to abort and return NULL if a signal is received wait‐ ing for a struct sf_buf to become available. SFB_NOWAIT Cause sf_buf_alloc() to return NULL rather than sleeping if a struct sf_buf is not immediately available. SFB_CPUPRIVATE 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(). Call sf_buf_kva() to return a kernel mapped address for the page. Call sf_buf_page() to return a pointer to the page originally passed into sf_buf_alloc(). Call sf_buf_free() to release the struct sf_buf reference. The caller is responsible for releasing any wiring they have previously acquired on the physical page; sf_buf_free() releases only the temporary kernel address space mapping, not the page itself. Uses of this interface include managing mappings of borrowed pages from user memory, such as in zero-copy socket I/O, or pages of memory from the buffer cache referenced by mbuf exter‐ nal storage for sendfile(2).


sendfile(2), vm_page_wire(9)


The struct sf_buf API was designed and implemented by Alan L. Cox. This manual page was written by Robert N. M. Watson.
BSD January 28, 2007 BSD
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sf_buf_free(9freebsd) referred by
refer to sendfile(2) | sf_buf(9freebsd) | vm_page_wire(9freebsd)