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36 .Nd manage temporary kernel address space mapping for memory pages
40 .Fn sf_buf_alloc "struct vm_page *m" "int flags"
42 .Fn sf_buf_free "struct sf_buf *sf"
44 .Fn sf_buf_kva "struct sf_buf *sf"
46 .Fn sf_buf_page "struct sf_buf *sf"
50 interface, historically the
52 buffer interface, allows kernel subsystems to manage temporary kernel address
53 space mappings for physical memory pages.
54 On systems with a direct memory map region (allowing all physical pages to be
55 visible in the kernel address space at all times), the
57 will point to an address in the direct map region; on systems without a
58 direct memory map region, the
60 will manage a temporary kernel address space mapping valid for the lifetime
68 for a physical memory page.
70 is not responsible for arranging for the page to be present in physical
71 memory; the caller should already have arranged for the page to be wired,
74 Several flags may be passed to
76 .Bl -tag -width SFB_CPUPRIVATE
82 if a signal is received waiting for a
90 rather than sleeping if a
92 is not immediately available.
96 to only arrange that the temporary mapping be valid on the current CPU,
97 avoiding unnecessary TLB shootdowns for mappings that will only be accessed
98 on a single CPU at a time.
99 The caller must ensure that accesses to the virtual address occur only on the
102 was invoked, perhaps by using
108 to return a kernel mapped address for the page.
112 to return a pointer to the page originally passed into
120 The caller is responsible for releasing any wiring they have previously
121 acquired on the physical page;
123 releases only the temporary kernel address space mapping, not the page
126 Uses of this interface include managing mappings of borrowed pages from user
127 memory, such as in zero-copy socket I/O, or pages of memory from the buffer
128 cache referenced by mbuf external storage for
137 API was designed and implemented by
139 This manual page was written by
140 .An Robert N. M. Watson .