SIMPLE SOLUTIONS

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

Manage temporary kernel address space mapping for memory pages.

Chapter
January 28, 2007
SF_BUF(9)                         BSD 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 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).
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.
BSD January 28, 2007 BSD
This manual Reference Other manuals
sf_buf(9freebsd) referred by sf_buf_alloc(9freebsd) | sf_buf_free(9freebsd) | sf_buf_kva(9freebsd) | sf_buf_page(9freebsd)
refer to sendfile(2) | vm_page_wire(9freebsd)