Manual Pages  — SGLIST

sglist, sglist_alloc, sglist_append, sglist_append_bio, sglist_append_mbuf, sglist_append_mbuf_epg, sglist_append_phys, sglist_append_sglist, sglist_append_single_mbuf, sglist_append_uio, sglist_append_user, sglist_append_vmpages, sglist_build, sglist_clone, sglist_consume_uio, sglist_count, sglist_count_mbuf_epg, sglist_count_vmpages, sglist_free, sglist_hold, sglist_init, sglist_join, sglist_length, sglist_reset, sglist_slice, sglist_split – manage a scatter/gather list of physical memory addresses

SYNOPSIS DESCRIPTION Allocating and Initializing Lists Constructing Scatter/Gather Lists Manipulating Scatter/Gather Lists Miscellaneous Routines RETURN VALUES ERRORS SEE ALSO HISTORY

#include <sys/types.h>

#include <sys/sglist.h>

struct sglist *
sglist_alloc(int nsegs, int mflags);

int
sglist_append(struct sglist *sg, void *buf, size_t len);

int
sglist_append_bio(struct sglist *sg, struct bio *bp);

int
sglist_append_mbuf_epg(struct sglist *sg, struct mbuf *m, size_t offset, size_t len);

int
sglist_append_mbuf(struct sglist *sg, struct mbuf *m);

int
sglist_append_phys(struct sglist *sg, vm_paddr_t paddr, size_t len);

int
sglist_append_sglist(struct sglist *sg, struct sglist *source, size_t offset, size_t len);

int
sglist_append_single_mbuf(struct sglist *sg, struct mbuf *m);

int
sglist_append_uio(struct sglist *sg, struct uio *uio);

int
sglist_append_user(struct sglist *sg, void *buf, size_t len, struct thread *td);

int
sglist_append_vmpages(struct sglist *sg, vm_page_t *m, size_t pgoff, size_t len);

struct sglist *
sglist_build(void *buf, size_t len, int mflags);

struct sglist *
sglist_clone(struct sglist *sg, int mflags);

int
sglist_consume_uio(struct sglist *sg, struct uio *uio, size_t resid);

int
sglist_count(void *buf, size_t len);

int
sglist_count_mbuf_epg(struct mbuf *m, size_t offset, size_t len);

int
sglist_count_vmpages(vm_page_t *m, size_t pgoff, size_t len);

void
sglist_free(struct sglist *sg);

struct sglist *
sglist_hold(struct sglist *sg);

void
sglist_init(struct sglist *sg, int maxsegs, struct sglist_seg *segs);

int
sglist_join(struct sglist *first, struct sglist *second);

size_t
sglist_length(struct sglist *sg);

void
sglist_reset(struct sglist *sg);

int
sglist_slice(struct sglist *original, struct sglist **slice, size_t offset, size_t length, int mflags);

int
sglist_split(struct sglist *original, struct sglist **head, size_t length, int mflags);

The sglist API manages physical address ranges. Each list contains one or more elements. Each element contains a starting physical address and a length. Scatter/gather lists are read-only while they are shared. If one wishes to alter an existing scatter/gather list and does not hold the sole reference to the list, then one should create a new list instead of modifying the existing list.

Each scatter/gather list object contains a reference count. New lists are created with a single reference. New references are obtained by calling sglist_hold and are released by calling sglist_free.

Each sglist object consists of a header structure and a variable-length array of scatter/gather list elements. The sglist_alloc function allocates a new list that contains a header and nsegs scatter/gather list elements. The mflags argument can be set to either M_NOWAIT or M_WAITOK.

The sglist_count function returns the number of scatter/gather list elements needed to describe the physical address ranges mapped by a single kernel virtual address range. The kernel virtual address range starts at buf and is len bytes long.

The sglist_count_mbuf_epg function returns the number of scatter/gather list elements needed to describe the external multipage mbuf buffer m. The ranges start at an offset of offset relative to the start of the buffer and is len bytes long.

The sglist_count_vmpages function returns the number of scatter/gather list elements needed to describe the physical address ranges of a buffer backed by an array of virtual memory pages m. The buffer starts at an offset of pgoff bytes relative to the first page and is len bytes long.

The sglist_build function allocates a new scatter/gather list object that describes the physical address ranges mapped by a single kernel virtual address range. The kernel virtual address range starts at buf and is len bytes long. The mflags argument can be set to either M_NOWAIT or M_WAITOK.

The sglist_clone function returns a copy of an existing scatter/gather list object sg. The mflags argument can be set to either M_NOWAIT or M_WAITOK. This can be used to obtain a private copy of a scatter/gather list before modifying it.

The sglist_init function initializes a scatter/gather list header. The header is pointed to by sg and is initialized to manage an array of maxsegs scatter/gather list elements pointed to by segs. This can be used to initialize a scatter/gather list header whose storage is not provided by sglist_alloc. In that case, the caller should not call sglist_free to release its own reference and is responsible for ensuring all other references to the list are dropped before it releases the storage for sg and segs.

The sglist_join function appends physical address ranges from the scatter/gather list second onto first and then resets second to an empty list. It returns zero on success or an error on failure.

The sglist_split function splits an existing scatter/gather list into two lists. The first length bytes described by the list original are moved to a new list *head. If original describes a total address range that is smaller than length bytes, then all of the address ranges will be moved to the new list at *head and original will be an empty list. The caller may supply an existing scatter/gather list in *head. If so, the list must be empty. Otherwise, the caller may set *head to NULL in which case a new scatter/gather list will be allocated. In that case, mflags may be set to either M_NOWAIT or M_WAITOK. Note that since the original list is modified by this call, it must be a private list with no other references. The sglist_split function returns zero on success or an error on failure.

The sglist_slice function generates a new scatter/gather list from a sub-range of an existing scatter/gather list original. The sub-range to extract is specified by the offset and length parameters. The new scatter/gather list is stored in *slice. As with head for sglist_join, the caller may either provide an empty scatter/gather list, or it may set *slice to NULL in which case sglist_slice will allocate a new list subject to mflags. Unlike sglist_split, sglist_slice does not modify original and does not require it to be a private list. The sglist_split function returns zero on success or an error on failure.

The sglist_reset function clears the scatter/gather list sg so that it no longer maps any address ranges. This can allow reuse of a single scatter/gather list object for multiple requests.

The sglist_length function returns the total length of the physical address ranges described by the scatter/gather list sg.

The sglist_alloc, sglist_build, and sglist_clone functions return a new scatter/gather list on success or NULL on failure.

The sglist_append family of functions and the sglist_consume_uio, sglist_join, sglist_slice, and sglist_split functions return zero on success or an error on failure.

The sglist_count family of functions return a count of scatter/gather list elements.

The sglist_length function returns a count of address space described by a scatter/gather list in bytes.

The sglist_append functions return the following errors on failure:

[EINVAL]
	The scatter/gather list has zero segments.
[EFBIG]
	There are not enough available segments in the scatter/gather list to append the specified physical address ranges.

The sglist_consume_uio function returns the following error on failure:

[EINVAL]
	The scatter/gather list has zero segments.

The sglist_join function returns the following error on failure:

[EFBIG]
	There are not enough available segments in the scatter/gather list first to append the physical address ranges from second.

The sglist_slice function returns the following errors on failure:

[EINVAL]
	The original scatter/gather list does not describe enough address space to cover the requested sub-range.
[EINVAL]
	The caller-supplied scatter/gather list in *slice is not empty.
[ENOMEM]
	An attempt to allocate a new scatter/gather list with M_NOWAIT set in mflags failed.
[EFBIG]
	There are not enough available segments in the caller-supplied scatter/gather list in *slice to describe the requested physical address ranges.

The sglist_split function returns the following errors on failure:

[EDOOFUS]
	The original scatter/gather list has more than one reference.
[EINVAL]
	The caller-supplied scatter/gather list in *head is not empty.
[ENOMEM]
	An attempt to allocate a new scatter/gather list with M_NOWAIT set in mflags failed.
[EFBIG]
	There are not enough available segments in the caller-supplied scatter/gather list in *head to describe the requested physical address ranges.

This API was first introduced in FreeBSD 8.0 .