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linux/lib/scatterlist.c
David Howells db0aa2e956
mm: Define struct folio_queue and ITER_FOLIOQ to handle a sequence of folios 
Define a data structure, struct folio_queue, to represent a sequence of
folios and a kernel-internal I/O iterator type, ITER_FOLIOQ, to allow a
list of folio_queue structures to be used to provide a buffer to
iov_iter-taking functions, such as sendmsg and recvmsg.

The folio_queue structure looks like:

	struct folio_queue {
		struct folio_batch	vec;
		u8			orders[PAGEVEC_SIZE];
		struct folio_queue	*next;
		struct folio_queue	*prev;
		unsigned long		marks;
		unsigned long		marks2;
	};

It does not use a list_head so that next and/or prev can be set to NULL at
the ends of the list, allowing iov_iter-handling routines to determine that
they *are* the ends without needing to store a head pointer in the iov_iter
struct.

A folio_batch struct is used to hold the folio pointers which allows the
batch to be passed to batch handling functions.  Two mark bits are
available per slot.  The intention is to use at least one of them to mark
folios that need putting, but that might not be ultimately necessary.
Accessor functions are used to access the slots to do the masking and an
additional accessor function is used to indicate the size of the array.

The order of each folio is also stored in the structure to avoid the need
for iov_iter_advance() and iov_iter_revert() to have to query each folio to
find its size.

With careful barriering, this can be used as an extending buffer with new
folios inserted and new folio_queue structs added without the need for a
lock.  Further, provided we always keep at least one struct in the buffer,
we can also remove consumed folios and consumed structs from the head end
as we without the need for locks.

[Questions/thoughts]

 (1) To manage this, I need a head pointer, a tail pointer, a tail slot
     number (assuming insertion happens at the tail end and the next
     pointers point from head to tail).  Should I put these into a struct
     of their own, say "folio_queue_head" or "rolling_buffer"?

     I will end up with two of these in netfs_io_request eventually, one
     keeping track of the pagecache I'm dealing with for buffered I/O and
     the other to hold a bounce buffer when we need one.

 (2) Should I make the slots {folio,off,len} or bio_vec?

 (3) This is intended to replace ITER_XARRAY eventually.  Using an xarray
     in I/O iteration requires the taking of the RCU read lock, doing
     copying under the RCU read lock, walking the xarray (which may change
     under us), handling retries and dealing with special values.

     The advantage of ITER_XARRAY is that when we're dealing with the
     pagecache directly, we don't need any allocation - but if we're doing
     encrypted comms, there's a good chance we'd be using a bounce buffer
     anyway.

     This will require afs, erofs, cifs, orangefs and fscache to be
     converted to not use this.  afs still uses it for dirs and symlinks;
     some of erofs usages should be easy to change, but there's one which
     won't be so easy; ceph's use via fscache can be fixed by porting ceph
     to netfslib; cifs is using xarray as a bounce buffer - that can be
     moved to use sheaves instead; and orangefs has a similar problem to
     erofs - maybe orangefs could use netfslib?

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: Steve French <sfrench@samba.org>
cc: Ilya Dryomov <idryomov@gmail.com>
cc: Gao Xiang <xiang@kernel.org>
cc: Mike Marshall <hubcap@omnibond.com>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
cc: linux-afs@lists.infradead.org
cc: linux-cifs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: linux-erofs@lists.ozlabs.org
cc: devel@lists.orangefs.org
Link: https://lore.kernel.org/r/20240814203850.2240469-13-dhowells@redhat.com/ # v2
Signed-off-by: Christian Brauner <brauner@kernel.org>
2024-09-12 12:20:21 +02:00

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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com>
*
* Scatterlist handling helpers.
*/
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/scatterlist.h>
#include <linux/highmem.h>
#include <linux/kmemleak.h>
#include <linux/bvec.h>
#include <linux/uio.h>
#include <linux/folio_queue.h>
/**
* sg_next - return the next scatterlist entry in a list
* @sg: The current sg entry
*
* Description:
* Usually the next entry will be @sg@ + 1, but if this sg element is part
* of a chained scatterlist, it could jump to the start of a new
* scatterlist array.
*
**/
struct scatterlist *sg_next(struct scatterlist *sg)
{
if (sg_is_last(sg))
return NULL;
sg++;
if (unlikely(sg_is_chain(sg)))
sg = sg_chain_ptr(sg);
return sg;
}
EXPORT_SYMBOL(sg_next);
/**
* sg_nents - return total count of entries in scatterlist
* @sg: The scatterlist
*
* Description:
* Allows to know how many entries are in sg, taking into account
* chaining as well
*
**/
int sg_nents(struct scatterlist *sg)
{
int nents;
for (nents = 0; sg; sg = sg_next(sg))
nents++;
return nents;
}
EXPORT_SYMBOL(sg_nents);
/**
* sg_nents_for_len - return total count of entries in scatterlist
* needed to satisfy the supplied length
* @sg: The scatterlist
* @len: The total required length
*
* Description:
* Determines the number of entries in sg that are required to meet
* the supplied length, taking into account chaining as well
*
* Returns:
* the number of sg entries needed, negative error on failure
*
**/
int sg_nents_for_len(struct scatterlist *sg, u64 len)
{
int nents;
u64 total;
if (!len)
return 0;
for (nents = 0, total = 0; sg; sg = sg_next(sg)) {
nents++;
total += sg->length;
if (total >= len)
return nents;
}
return -EINVAL;
}
EXPORT_SYMBOL(sg_nents_for_len);
/**
* sg_last - return the last scatterlist entry in a list
* @sgl: First entry in the scatterlist
* @nents: Number of entries in the scatterlist
*
* Description:
* Should only be used casually, it (currently) scans the entire list
* to get the last entry.
*
* Note that the @sgl@ pointer passed in need not be the first one,
* the important bit is that @nents@ denotes the number of entries that
* exist from @sgl@.
*
**/
struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
{
struct scatterlist *sg, *ret = NULL;
unsigned int i;
for_each_sg(sgl, sg, nents, i)
ret = sg;
BUG_ON(!sg_is_last(ret));
return ret;
}
EXPORT_SYMBOL(sg_last);
/**
* sg_init_table - Initialize SG table
* @sgl: The SG table
* @nents: Number of entries in table
*
* Notes:
* If this is part of a chained sg table, sg_mark_end() should be
* used only on the last table part.
*
**/
void sg_init_table(struct scatterlist *sgl, unsigned int nents)
{
memset(sgl, 0, sizeof(*sgl) * nents);
sg_init_marker(sgl, nents);
}
EXPORT_SYMBOL(sg_init_table);
/**
* sg_init_one - Initialize a single entry sg list
* @sg: SG entry
* @buf: Virtual address for IO
* @buflen: IO length
*
**/
void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
{
sg_init_table(sg, 1);
sg_set_buf(sg, buf, buflen);
}
EXPORT_SYMBOL(sg_init_one);
/*
* The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
* helpers.
*/
static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
{
if (nents == SG_MAX_SINGLE_ALLOC) {
/*
* Kmemleak doesn't track page allocations as they are not
* commonly used (in a raw form) for kernel data structures.
* As we chain together a list of pages and then a normal
* kmalloc (tracked by kmemleak), in order to for that last
* allocation not to become decoupled (and thus a
* false-positive) we need to inform kmemleak of all the
* intermediate allocations.
*/
void *ptr = (void *) __get_free_page(gfp_mask);
kmemleak_alloc(ptr, PAGE_SIZE, 1, gfp_mask);
return ptr;
} else
return kmalloc_array(nents, sizeof(struct scatterlist),
gfp_mask);
}
static void sg_kfree(struct scatterlist *sg, unsigned int nents)
{
if (nents == SG_MAX_SINGLE_ALLOC) {
kmemleak_free(sg);
free_page((unsigned long) sg);
} else
kfree(sg);
}
/**
* __sg_free_table - Free a previously mapped sg table
* @table: The sg table header to use
* @max_ents: The maximum number of entries per single scatterlist
* @nents_first_chunk: Number of entries int the (preallocated) first
* scatterlist chunk, 0 means no such preallocated first chunk
* @free_fn: Free function
* @num_ents: Number of entries in the table
*
* Description:
* Free an sg table previously allocated and setup with
* __sg_alloc_table(). The @max_ents value must be identical to
* that previously used with __sg_alloc_table().
*
**/
void __sg_free_table(struct sg_table *table, unsigned int max_ents,
unsigned int nents_first_chunk, sg_free_fn *free_fn,
unsigned int num_ents)
{
struct scatterlist *sgl, *next;
unsigned curr_max_ents = nents_first_chunk ?: max_ents;
if (unlikely(!table->sgl))
return;
sgl = table->sgl;
while (num_ents) {
unsigned int alloc_size = num_ents;
unsigned int sg_size;
/*
* If we have more than max_ents segments left,
* then assign 'next' to the sg table after the current one.
* sg_size is then one less than alloc size, since the last
* element is the chain pointer.
*/
if (alloc_size > curr_max_ents) {
next = sg_chain_ptr(&sgl[curr_max_ents - 1]);
alloc_size = curr_max_ents;
sg_size = alloc_size - 1;
} else {
sg_size = alloc_size;
next = NULL;
}
num_ents -= sg_size;
if (nents_first_chunk)
nents_first_chunk = 0;
else
free_fn(sgl, alloc_size);
sgl = next;
curr_max_ents = max_ents;
}
table->sgl = NULL;
}
EXPORT_SYMBOL(__sg_free_table);
/**
* sg_free_append_table - Free a previously allocated append sg table.
* @table: The mapped sg append table header
*
**/
void sg_free_append_table(struct sg_append_table *table)
{
__sg_free_table(&table->sgt, SG_MAX_SINGLE_ALLOC, 0, sg_kfree,
table->total_nents);
}
EXPORT_SYMBOL(sg_free_append_table);
/**
* sg_free_table - Free a previously allocated sg table
* @table: The mapped sg table header
*
**/
void sg_free_table(struct sg_table *table)
{
__sg_free_table(table, SG_MAX_SINGLE_ALLOC, 0, sg_kfree,
table->orig_nents);
}
EXPORT_SYMBOL(sg_free_table);
/**
* __sg_alloc_table - Allocate and initialize an sg table with given allocator
* @table: The sg table header to use
* @nents: Number of entries in sg list
* @max_ents: The maximum number of entries the allocator returns per call
* @first_chunk: first SGL if preallocated (may be %NULL)
* @nents_first_chunk: Number of entries in the (preallocated) first
* scatterlist chunk, 0 means no such preallocated chunk provided by user
* @gfp_mask: GFP allocation mask
* @alloc_fn: Allocator to use
*
* Description:
* This function returns a @table @nents long. The allocator is
* defined to return scatterlist chunks of maximum size @max_ents.
* Thus if @nents is bigger than @max_ents, the scatterlists will be
* chained in units of @max_ents.
*
* Notes:
* If this function returns non-0 (eg failure), the caller must call
* __sg_free_table() to cleanup any leftover allocations.
*
**/
int __sg_alloc_table(struct sg_table *table, unsigned int nents,
unsigned int max_ents, struct scatterlist *first_chunk,
unsigned int nents_first_chunk, gfp_t gfp_mask,
sg_alloc_fn *alloc_fn)
{
struct scatterlist *sg, *prv;
unsigned int left;
unsigned curr_max_ents = nents_first_chunk ?: max_ents;
unsigned prv_max_ents;
memset(table, 0, sizeof(*table));
if (nents == 0)
return -EINVAL;
#ifdef CONFIG_ARCH_NO_SG_CHAIN
if (WARN_ON_ONCE(nents > max_ents))
return -EINVAL;
#endif
left = nents;
prv = NULL;
do {
unsigned int sg_size, alloc_size = left;
if (alloc_size > curr_max_ents) {
alloc_size = curr_max_ents;
sg_size = alloc_size - 1;
} else
sg_size = alloc_size;
left -= sg_size;
if (first_chunk) {
sg = first_chunk;
first_chunk = NULL;
} else {
sg = alloc_fn(alloc_size, gfp_mask);
}
if (unlikely(!sg)) {
/*
* Adjust entry count to reflect that the last
* entry of the previous table won't be used for
* linkage. Without this, sg_kfree() may get
* confused.
*/
if (prv)
table->nents = ++table->orig_nents;
return -ENOMEM;
}
sg_init_table(sg, alloc_size);
table->nents = table->orig_nents += sg_size;
/*
* If this is the first mapping, assign the sg table header.
* If this is not the first mapping, chain previous part.
*/
if (prv)
sg_chain(prv, prv_max_ents, sg);
else
table->sgl = sg;
/*
* If no more entries after this one, mark the end
*/
if (!left)
sg_mark_end(&sg[sg_size - 1]);
prv = sg;
prv_max_ents = curr_max_ents;
curr_max_ents = max_ents;
} while (left);
return 0;
}
EXPORT_SYMBOL(__sg_alloc_table);
/**
* sg_alloc_table - Allocate and initialize an sg table
* @table: The sg table header to use
* @nents: Number of entries in sg list
* @gfp_mask: GFP allocation mask
*
* Description:
* Allocate and initialize an sg table. If @nents@ is larger than
* SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
*
**/
int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
{
int ret;
ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
NULL, 0, gfp_mask, sg_kmalloc);
if (unlikely(ret))
sg_free_table(table);
return ret;
}
EXPORT_SYMBOL(sg_alloc_table);
static struct scatterlist *get_next_sg(struct sg_append_table *table,
struct scatterlist *cur,
unsigned long needed_sges,
gfp_t gfp_mask)
{
struct scatterlist *new_sg, *next_sg;
unsigned int alloc_size;
if (cur) {
next_sg = sg_next(cur);
/* Check if last entry should be keeped for chainning */
if (!sg_is_last(next_sg) || needed_sges == 1)
return next_sg;
}
alloc_size = min_t(unsigned long, needed_sges, SG_MAX_SINGLE_ALLOC);
new_sg = sg_kmalloc(alloc_size, gfp_mask);
if (!new_sg)
return ERR_PTR(-ENOMEM);
sg_init_table(new_sg, alloc_size);
if (cur) {
table->total_nents += alloc_size - 1;
__sg_chain(next_sg, new_sg);
} else {
table->sgt.sgl = new_sg;
table->total_nents = alloc_size;
}
return new_sg;
}
static bool pages_are_mergeable(struct page *a, struct page *b)
{
if (page_to_pfn(a) != page_to_pfn(b) + 1)
return false;
if (!zone_device_pages_have_same_pgmap(a, b))
return false;
return true;
}
/**
* sg_alloc_append_table_from_pages - Allocate and initialize an append sg
* table from an array of pages
* @sgt_append: The sg append table to use
* @pages: Pointer to an array of page pointers
* @n_pages: Number of pages in the pages array
* @offset: Offset from start of the first page to the start of a buffer
* @size: Number of valid bytes in the buffer (after offset)
* @max_segment: Maximum size of a scatterlist element in bytes
* @left_pages: Left pages caller have to set after this call
* @gfp_mask: GFP allocation mask
*
* Description:
* In the first call it allocate and initialize an sg table from a list of
* pages, else reuse the scatterlist from sgt_append. Contiguous ranges of
* the pages are squashed into a single scatterlist entry up to the maximum
* size specified in @max_segment. A user may provide an offset at a start
* and a size of valid data in a buffer specified by the page array. The
* returned sg table is released by sg_free_append_table
*
* Returns:
* 0 on success, negative error on failure
*
* Notes:
* If this function returns non-0 (eg failure), the caller must call
* sg_free_append_table() to cleanup any leftover allocations.
*
* In the fist call, sgt_append must by initialized.
*/
int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
struct page **pages, unsigned int n_pages, unsigned int offset,
unsigned long size, unsigned int max_segment,
unsigned int left_pages, gfp_t gfp_mask)
{
unsigned int chunks, cur_page, seg_len, i, prv_len = 0;
unsigned int added_nents = 0;
struct scatterlist *s = sgt_append->prv;
struct page *last_pg;
/*
* The algorithm below requires max_segment to be aligned to PAGE_SIZE
* otherwise it can overshoot.
*/
max_segment = ALIGN_DOWN(max_segment, PAGE_SIZE);
if (WARN_ON(max_segment < PAGE_SIZE))
return -EINVAL;
if (IS_ENABLED(CONFIG_ARCH_NO_SG_CHAIN) && sgt_append->prv)
return -EOPNOTSUPP;
if (sgt_append->prv) {
unsigned long next_pfn = (page_to_phys(sg_page(sgt_append->prv)) +
sgt_append->prv->offset + sgt_append->prv->length) / PAGE_SIZE;
if (WARN_ON(offset))
return -EINVAL;
/* Merge contiguous pages into the last SG */
prv_len = sgt_append->prv->length;
if (page_to_pfn(pages[0]) == next_pfn) {
last_pg = pfn_to_page(next_pfn - 1);
while (n_pages && pages_are_mergeable(pages[0], last_pg)) {
if (sgt_append->prv->length + PAGE_SIZE > max_segment)
break;
sgt_append->prv->length += PAGE_SIZE;
last_pg = pages[0];
pages++;
n_pages--;
}
if (!n_pages)
goto out;
}
}
/* compute number of contiguous chunks */
chunks = 1;
seg_len = 0;
for (i = 1; i < n_pages; i++) {
seg_len += PAGE_SIZE;
if (seg_len >= max_segment ||
!pages_are_mergeable(pages[i], pages[i - 1])) {
chunks++;
seg_len = 0;
}
}
/* merging chunks and putting them into the scatterlist */
cur_page = 0;
for (i = 0; i < chunks; i++) {
unsigned int j, chunk_size;
/* look for the end of the current chunk */
seg_len = 0;
for (j = cur_page + 1; j < n_pages; j++) {
seg_len += PAGE_SIZE;
if (seg_len >= max_segment ||
!pages_are_mergeable(pages[j], pages[j - 1]))
break;
}
/* Pass how many chunks might be left */
s = get_next_sg(sgt_append, s, chunks - i + left_pages,
gfp_mask);
if (IS_ERR(s)) {
/*
* Adjust entry length to be as before function was
* called.
*/
if (sgt_append->prv)
sgt_append->prv->length = prv_len;
return PTR_ERR(s);
}
chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
sg_set_page(s, pages[cur_page],
min_t(unsigned long, size, chunk_size), offset);
added_nents++;
size -= chunk_size;
offset = 0;
cur_page = j;
}
sgt_append->sgt.nents += added_nents;
sgt_append->sgt.orig_nents = sgt_append->sgt.nents;
sgt_append->prv = s;
out:
if (!left_pages)
sg_mark_end(s);
return 0;
}
EXPORT_SYMBOL(sg_alloc_append_table_from_pages);
/**
* sg_alloc_table_from_pages_segment - Allocate and initialize an sg table from
* an array of pages and given maximum
* segment.
* @sgt: The sg table header to use
* @pages: Pointer to an array of page pointers
* @n_pages: Number of pages in the pages array
* @offset: Offset from start of the first page to the start of a buffer
* @size: Number of valid bytes in the buffer (after offset)
* @max_segment: Maximum size of a scatterlist element in bytes
* @gfp_mask: GFP allocation mask
*
* Description:
* Allocate and initialize an sg table from a list of pages. Contiguous
* ranges of the pages are squashed into a single scatterlist node up to the
* maximum size specified in @max_segment. A user may provide an offset at a
* start and a size of valid data in a buffer specified by the page array.
*
* The returned sg table is released by sg_free_table.
*
* Returns:
* 0 on success, negative error on failure
*/
int sg_alloc_table_from_pages_segment(struct sg_table *sgt, struct page **pages,
unsigned int n_pages, unsigned int offset,
unsigned long size, unsigned int max_segment,
gfp_t gfp_mask)
{
struct sg_append_table append = {};
int err;
err = sg_alloc_append_table_from_pages(&append, pages, n_pages, offset,
size, max_segment, 0, gfp_mask);
if (err) {
sg_free_append_table(&append);
return err;
}
memcpy(sgt, &append.sgt, sizeof(*sgt));
WARN_ON(append.total_nents != sgt->orig_nents);
return 0;
}
EXPORT_SYMBOL(sg_alloc_table_from_pages_segment);
#ifdef CONFIG_SGL_ALLOC
/**
* sgl_alloc_order - allocate a scatterlist and its pages
* @length: Length in bytes of the scatterlist. Must be at least one
* @order: Second argument for alloc_pages()
* @chainable: Whether or not to allocate an extra element in the scatterlist
* for scatterlist chaining purposes
* @gfp: Memory allocation flags
* @nent_p: [out] Number of entries in the scatterlist that have pages
*
* Returns: A pointer to an initialized scatterlist or %NULL upon failure.
*/
struct scatterlist *sgl_alloc_order(unsigned long long length,
unsigned int order, bool chainable,
gfp_t gfp, unsigned int *nent_p)
{
struct scatterlist *sgl, *sg;
struct page *page;
unsigned int nent, nalloc;
u32 elem_len;
nent = round_up(length, PAGE_SIZE << order) >> (PAGE_SHIFT + order);
/* Check for integer overflow */
if (length > (nent << (PAGE_SHIFT + order)))
return NULL;
nalloc = nent;
if (chainable) {
/* Check for integer overflow */
if (nalloc + 1 < nalloc)
return NULL;
nalloc++;
}
sgl = kmalloc_array(nalloc, sizeof(struct scatterlist),
gfp & ~GFP_DMA);
if (!sgl)
return NULL;
sg_init_table(sgl, nalloc);
sg = sgl;
while (length) {
elem_len = min_t(u64, length, PAGE_SIZE << order);
page = alloc_pages(gfp, order);
if (!page) {
sgl_free_order(sgl, order);
return NULL;
}
sg_set_page(sg, page, elem_len, 0);
length -= elem_len;
sg = sg_next(sg);
}
WARN_ONCE(length, "length = %lld\n", length);
if (nent_p)
*nent_p = nent;
return sgl;
}
EXPORT_SYMBOL(sgl_alloc_order);
/**
* sgl_alloc - allocate a scatterlist and its pages
* @length: Length in bytes of the scatterlist
* @gfp: Memory allocation flags
* @nent_p: [out] Number of entries in the scatterlist
*
* Returns: A pointer to an initialized scatterlist or %NULL upon failure.
*/
struct scatterlist *sgl_alloc(unsigned long long length, gfp_t gfp,
unsigned int *nent_p)
{
return sgl_alloc_order(length, 0, false, gfp, nent_p);
}
EXPORT_SYMBOL(sgl_alloc);
/**
* sgl_free_n_order - free a scatterlist and its pages
* @sgl: Scatterlist with one or more elements
* @nents: Maximum number of elements to free
* @order: Second argument for __free_pages()
*
* Notes:
* - If several scatterlists have been chained and each chain element is
* freed separately then it's essential to set nents correctly to avoid that a
* page would get freed twice.
* - All pages in a chained scatterlist can be freed at once by setting @nents
* to a high number.
*/
void sgl_free_n_order(struct scatterlist *sgl, int nents, int order)
{
struct scatterlist *sg;
struct page *page;
int i;
for_each_sg(sgl, sg, nents, i) {
if (!sg)
break;
page = sg_page(sg);
if (page)
__free_pages(page, order);
}
kfree(sgl);
}
EXPORT_SYMBOL(sgl_free_n_order);
/**
* sgl_free_order - free a scatterlist and its pages
* @sgl: Scatterlist with one or more elements
* @order: Second argument for __free_pages()
*/
void sgl_free_order(struct scatterlist *sgl, int order)
{
sgl_free_n_order(sgl, INT_MAX, order);
}
EXPORT_SYMBOL(sgl_free_order);
/**
* sgl_free - free a scatterlist and its pages
* @sgl: Scatterlist with one or more elements
*/
void sgl_free(struct scatterlist *sgl)
{
sgl_free_order(sgl, 0);
}
EXPORT_SYMBOL(sgl_free);
#endif /* CONFIG_SGL_ALLOC */
void __sg_page_iter_start(struct sg_page_iter *piter,
struct scatterlist *sglist, unsigned int nents,
unsigned long pgoffset)
{
piter->__pg_advance = 0;
piter->__nents = nents;
piter->sg = sglist;
piter->sg_pgoffset = pgoffset;
}
EXPORT_SYMBOL(__sg_page_iter_start);
static int sg_page_count(struct scatterlist *sg)
{
return PAGE_ALIGN(sg->offset + sg->length) >> PAGE_SHIFT;
}
bool __sg_page_iter_next(struct sg_page_iter *piter)
{
if (!piter->__nents || !piter->sg)
return false;
piter->sg_pgoffset += piter->__pg_advance;
piter->__pg_advance = 1;
while (piter->sg_pgoffset >= sg_page_count(piter->sg)) {
piter->sg_pgoffset -= sg_page_count(piter->sg);
piter->sg = sg_next(piter->sg);
if (!--piter->__nents || !piter->sg)
return false;
}
return true;
}
EXPORT_SYMBOL(__sg_page_iter_next);
static int sg_dma_page_count(struct scatterlist *sg)
{
return PAGE_ALIGN(sg->offset + sg_dma_len(sg)) >> PAGE_SHIFT;
}
bool __sg_page_iter_dma_next(struct sg_dma_page_iter *dma_iter)
{
struct sg_page_iter *piter = &dma_iter->base;
if (!piter->__nents || !piter->sg)
return false;
piter->sg_pgoffset += piter->__pg_advance;
piter->__pg_advance = 1;
while (piter->sg_pgoffset >= sg_dma_page_count(piter->sg)) {
piter->sg_pgoffset -= sg_dma_page_count(piter->sg);
piter->sg = sg_next(piter->sg);
if (!--piter->__nents || !piter->sg)
return false;
}
return true;
}
EXPORT_SYMBOL(__sg_page_iter_dma_next);
/**
* sg_miter_start - start mapping iteration over a sg list
* @miter: sg mapping iter to be started
* @sgl: sg list to iterate over
* @nents: number of sg entries
* @flags: sg iterator flags
*
* Description:
* Starts mapping iterator @miter.
*
* Context:
* Don't care.
*/
void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
unsigned int nents, unsigned int flags)
{
memset(miter, 0, sizeof(struct sg_mapping_iter));
__sg_page_iter_start(&miter->piter, sgl, nents, 0);
WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
miter->__flags = flags;
}
EXPORT_SYMBOL(sg_miter_start);
static bool sg_miter_get_next_page(struct sg_mapping_iter *miter)
{
if (!miter->__remaining) {
struct scatterlist *sg;
if (!__sg_page_iter_next(&miter->piter))
return false;
sg = miter->piter.sg;
miter->__offset = miter->piter.sg_pgoffset ? 0 : sg->offset;
miter->piter.sg_pgoffset += miter->__offset >> PAGE_SHIFT;
miter->__offset &= PAGE_SIZE - 1;
miter->__remaining = sg->offset + sg->length -
(miter->piter.sg_pgoffset << PAGE_SHIFT) -
miter->__offset;
miter->__remaining = min_t(unsigned long, miter->__remaining,
PAGE_SIZE - miter->__offset);
}
return true;
}
/**
* sg_miter_skip - reposition mapping iterator
* @miter: sg mapping iter to be skipped
* @offset: number of bytes to plus the current location
*
* Description:
* Sets the offset of @miter to its current location plus @offset bytes.
* If mapping iterator @miter has been proceeded by sg_miter_next(), this
* stops @miter.
*
* Context:
* Don't care.
*
* Returns:
* true if @miter contains the valid mapping. false if end of sg
* list is reached.
*/
bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset)
{
sg_miter_stop(miter);
while (offset) {
off_t consumed;
if (!sg_miter_get_next_page(miter))
return false;
consumed = min_t(off_t, offset, miter->__remaining);
miter->__offset += consumed;
miter->__remaining -= consumed;
offset -= consumed;
}
return true;
}
EXPORT_SYMBOL(sg_miter_skip);
/**
* sg_miter_next - proceed mapping iterator to the next mapping
* @miter: sg mapping iter to proceed
*
* Description:
* Proceeds @miter to the next mapping. @miter should have been started
* using sg_miter_start(). On successful return, @miter->page,
* @miter->addr and @miter->length point to the current mapping.
*
* Context:
* May sleep if !SG_MITER_ATOMIC.
*
* Returns:
* true if @miter contains the next mapping. false if end of sg
* list is reached.
*/
bool sg_miter_next(struct sg_mapping_iter *miter)
{
sg_miter_stop(miter);
/*
* Get to the next page if necessary.
* __remaining, __offset is adjusted by sg_miter_stop
*/
if (!sg_miter_get_next_page(miter))
return false;
miter->page = sg_page_iter_page(&miter->piter);
miter->consumed = miter->length = miter->__remaining;
if (miter->__flags & SG_MITER_ATOMIC)
miter->addr = kmap_atomic(miter->page) + miter->__offset;
else
miter->addr = kmap(miter->page) + miter->__offset;
return true;
}
EXPORT_SYMBOL(sg_miter_next);
/**
* sg_miter_stop - stop mapping iteration
* @miter: sg mapping iter to be stopped
*
* Description:
* Stops mapping iterator @miter. @miter should have been started
* using sg_miter_start(). A stopped iteration can be resumed by
* calling sg_miter_next() on it. This is useful when resources (kmap)
* need to be released during iteration.
*
* Context:
* Don't care otherwise.
*/
void sg_miter_stop(struct sg_mapping_iter *miter)
{
WARN_ON(miter->consumed > miter->length);
/* drop resources from the last iteration */
if (miter->addr) {
miter->__offset += miter->consumed;
miter->__remaining -= miter->consumed;
if (miter->__flags & SG_MITER_TO_SG)
flush_dcache_page(miter->page);
if (miter->__flags & SG_MITER_ATOMIC) {
WARN_ON_ONCE(!pagefault_disabled());
kunmap_atomic(miter->addr);
} else
kunmap(miter->page);
miter->page = NULL;
miter->addr = NULL;
miter->length = 0;
miter->consumed = 0;
}
}
EXPORT_SYMBOL(sg_miter_stop);
/**
* sg_copy_buffer - Copy data between a linear buffer and an SG list
* @sgl: The SG list
* @nents: Number of SG entries
* @buf: Where to copy from
* @buflen: The number of bytes to copy
* @skip: Number of bytes to skip before copying
* @to_buffer: transfer direction (true == from an sg list to a
* buffer, false == from a buffer to an sg list)
*
* Returns the number of copied bytes.
*
**/
size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void *buf,
size_t buflen, off_t skip, bool to_buffer)
{
unsigned int offset = 0;
struct sg_mapping_iter miter;
unsigned int sg_flags = SG_MITER_ATOMIC;
if (to_buffer)
sg_flags |= SG_MITER_FROM_SG;
else
sg_flags |= SG_MITER_TO_SG;
sg_miter_start(&miter, sgl, nents, sg_flags);
if (!sg_miter_skip(&miter, skip))
return 0;
while ((offset < buflen) && sg_miter_next(&miter)) {
unsigned int len;
len = min(miter.length, buflen - offset);
if (to_buffer)
memcpy(buf + offset, miter.addr, len);
else
memcpy(miter.addr, buf + offset, len);
offset += len;
}
sg_miter_stop(&miter);
return offset;
}
EXPORT_SYMBOL(sg_copy_buffer);
/**
* sg_copy_from_buffer - Copy from a linear buffer to an SG list
* @sgl: The SG list
* @nents: Number of SG entries
* @buf: Where to copy from
* @buflen: The number of bytes to copy
*
* Returns the number of copied bytes.
*
**/
size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
const void *buf, size_t buflen)
{
return sg_copy_buffer(sgl, nents, (void *)buf, buflen, 0, false);
}
EXPORT_SYMBOL(sg_copy_from_buffer);
/**
* sg_copy_to_buffer - Copy from an SG list to a linear buffer
* @sgl: The SG list
* @nents: Number of SG entries
* @buf: Where to copy to
* @buflen: The number of bytes to copy
*
* Returns the number of copied bytes.
*
**/
size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
void *buf, size_t buflen)
{
return sg_copy_buffer(sgl, nents, buf, buflen, 0, true);
}
EXPORT_SYMBOL(sg_copy_to_buffer);
/**
* sg_pcopy_from_buffer - Copy from a linear buffer to an SG list
* @sgl: The SG list
* @nents: Number of SG entries
* @buf: Where to copy from
* @buflen: The number of bytes to copy
* @skip: Number of bytes to skip before copying
*
* Returns the number of copied bytes.
*
**/
size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
const void *buf, size_t buflen, off_t skip)
{
return sg_copy_buffer(sgl, nents, (void *)buf, buflen, skip, false);
}
EXPORT_SYMBOL(sg_pcopy_from_buffer);
/**
* sg_pcopy_to_buffer - Copy from an SG list to a linear buffer
* @sgl: The SG list
* @nents: Number of SG entries
* @buf: Where to copy to
* @buflen: The number of bytes to copy
* @skip: Number of bytes to skip before copying
*
* Returns the number of copied bytes.
*
**/
size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
void *buf, size_t buflen, off_t skip)
{
return sg_copy_buffer(sgl, nents, buf, buflen, skip, true);
}
EXPORT_SYMBOL(sg_pcopy_to_buffer);
/**
* sg_zero_buffer - Zero-out a part of a SG list
* @sgl: The SG list
* @nents: Number of SG entries
* @buflen: The number of bytes to zero out
* @skip: Number of bytes to skip before zeroing
*
* Returns the number of bytes zeroed.
**/
size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
size_t buflen, off_t skip)
{
unsigned int offset = 0;
struct sg_mapping_iter miter;
unsigned int sg_flags = SG_MITER_ATOMIC | SG_MITER_TO_SG;
sg_miter_start(&miter, sgl, nents, sg_flags);
if (!sg_miter_skip(&miter, skip))
return false;
while (offset < buflen && sg_miter_next(&miter)) {
unsigned int len;
len = min(miter.length, buflen - offset);
memset(miter.addr, 0, len);
offset += len;
}
sg_miter_stop(&miter);
return offset;
}
EXPORT_SYMBOL(sg_zero_buffer);
/*
* Extract and pin a list of up to sg_max pages from UBUF- or IOVEC-class
* iterators, and add them to the scatterlist.
*/
static ssize_t extract_user_to_sg(struct iov_iter *iter,
ssize_t maxsize,
struct sg_table *sgtable,
unsigned int sg_max,
iov_iter_extraction_t extraction_flags)
{
struct scatterlist *sg = sgtable->sgl + sgtable->nents;
struct page **pages;
unsigned int npages;
ssize_t ret = 0, res;
size_t len, off;
/* We decant the page list into the tail of the scatterlist */
pages = (void *)sgtable->sgl +
array_size(sg_max, sizeof(struct scatterlist));
pages -= sg_max;
do {
res = iov_iter_extract_pages(iter, &pages, maxsize, sg_max,
extraction_flags, &off);
if (res <= 0)
goto failed;
len = res;
maxsize -= len;
ret += len;
npages = DIV_ROUND_UP(off + len, PAGE_SIZE);
sg_max -= npages;
for (; npages > 0; npages--) {
struct page *page = *pages;
size_t seg = min_t(size_t, PAGE_SIZE - off, len);
*pages++ = NULL;
sg_set_page(sg, page, seg, off);
sgtable->nents++;
sg++;
len -= seg;
off = 0;
}
} while (maxsize > 0 && sg_max > 0);
return ret;
failed:
while (sgtable->nents > sgtable->orig_nents)
unpin_user_page(sg_page(&sgtable->sgl[--sgtable->nents]));
return res;
}
/*
* Extract up to sg_max pages from a BVEC-type iterator and add them to the
* scatterlist. The pages are not pinned.
*/
static ssize_t extract_bvec_to_sg(struct iov_iter *iter,
ssize_t maxsize,
struct sg_table *sgtable,
unsigned int sg_max,
iov_iter_extraction_t extraction_flags)
{
const struct bio_vec *bv = iter->bvec;
struct scatterlist *sg = sgtable->sgl + sgtable->nents;
unsigned long start = iter->iov_offset;
unsigned int i;
ssize_t ret = 0;
for (i = 0; i < iter->nr_segs; i++) {
size_t off, len;
len = bv[i].bv_len;
if (start >= len) {
start -= len;
continue;
}
len = min_t(size_t, maxsize, len - start);
off = bv[i].bv_offset + start;
sg_set_page(sg, bv[i].bv_page, len, off);
sgtable->nents++;
sg++;
sg_max--;
ret += len;
maxsize -= len;
if (maxsize <= 0 || sg_max == 0)
break;
start = 0;
}
if (ret > 0)
iov_iter_advance(iter, ret);
return ret;
}
/*
* Extract up to sg_max pages from a KVEC-type iterator and add them to the
* scatterlist. This can deal with vmalloc'd buffers as well as kmalloc'd or
* static buffers. The pages are not pinned.
*/
static ssize_t extract_kvec_to_sg(struct iov_iter *iter,
ssize_t maxsize,
struct sg_table *sgtable,
unsigned int sg_max,
iov_iter_extraction_t extraction_flags)
{
const struct kvec *kv = iter->kvec;
struct scatterlist *sg = sgtable->sgl + sgtable->nents;
unsigned long start = iter->iov_offset;
unsigned int i;
ssize_t ret = 0;
for (i = 0; i < iter->nr_segs; i++) {
struct page *page;
unsigned long kaddr;
size_t off, len, seg;
len = kv[i].iov_len;
if (start >= len) {
start -= len;
continue;
}
kaddr = (unsigned long)kv[i].iov_base + start;
off = kaddr & ~PAGE_MASK;
len = min_t(size_t, maxsize, len - start);
kaddr &= PAGE_MASK;
maxsize -= len;
ret += len;
do {
seg = min_t(size_t, len, PAGE_SIZE - off);
if (is_vmalloc_or_module_addr((void *)kaddr))
page = vmalloc_to_page((void *)kaddr);
else
page = virt_to_page((void *)kaddr);
sg_set_page(sg, page, len, off);
sgtable->nents++;
sg++;
sg_max--;
len -= seg;
kaddr += PAGE_SIZE;
off = 0;
} while (len > 0 && sg_max > 0);
if (maxsize <= 0 || sg_max == 0)
break;
start = 0;
}
if (ret > 0)
iov_iter_advance(iter, ret);
return ret;
}
/*
* Extract up to sg_max folios from an FOLIOQ-type iterator and add them to
* the scatterlist. The pages are not pinned.
*/
static ssize_t extract_folioq_to_sg(struct iov_iter *iter,
ssize_t maxsize,
struct sg_table *sgtable,
unsigned int sg_max,
iov_iter_extraction_t extraction_flags)
{
const struct folio_queue *folioq = iter->folioq;
struct scatterlist *sg = sgtable->sgl + sgtable->nents;
unsigned int slot = iter->folioq_slot;
ssize_t ret = 0;
size_t offset = iter->iov_offset;
BUG_ON(!folioq);
if (slot >= folioq_nr_slots(folioq)) {
folioq = folioq->next;
if (WARN_ON_ONCE(!folioq))
return 0;
slot = 0;
}
do {
struct folio *folio = folioq_folio(folioq, slot);
size_t fsize = folioq_folio_size(folioq, slot);
if (offset < fsize) {
size_t part = umin(maxsize - ret, fsize - offset);
sg_set_page(sg, folio_page(folio, 0), part, offset);
sgtable->nents++;
sg++;
sg_max--;
offset += part;
ret += part;
}
if (offset >= fsize) {
offset = 0;
slot++;
if (slot >= folioq_nr_slots(folioq)) {
if (!folioq->next) {
WARN_ON_ONCE(ret < iter->count);
break;
}
folioq = folioq->next;
slot = 0;
}
}
} while (sg_max > 0 && ret < maxsize);
iter->folioq = folioq;
iter->folioq_slot = slot;
iter->iov_offset = offset;
iter->count -= ret;
return ret;
}
/*
* Extract up to sg_max folios from an XARRAY-type iterator and add them to
* the scatterlist. The pages are not pinned.
*/
static ssize_t extract_xarray_to_sg(struct iov_iter *iter,
ssize_t maxsize,
struct sg_table *sgtable,
unsigned int sg_max,
iov_iter_extraction_t extraction_flags)
{
struct scatterlist *sg = sgtable->sgl + sgtable->nents;
struct xarray *xa = iter->xarray;
struct folio *folio;
loff_t start = iter->xarray_start + iter->iov_offset;
pgoff_t index = start / PAGE_SIZE;
ssize_t ret = 0;
size_t offset, len;
XA_STATE(xas, xa, index);
rcu_read_lock();
xas_for_each(&xas, folio, ULONG_MAX) {
if (xas_retry(&xas, folio))
continue;
if (WARN_ON(xa_is_value(folio)))
break;
if (WARN_ON(folio_test_hugetlb(folio)))
break;
offset = offset_in_folio(folio, start);
len = min_t(size_t, maxsize, folio_size(folio) - offset);
sg_set_page(sg, folio_page(folio, 0), len, offset);
sgtable->nents++;
sg++;
sg_max--;
maxsize -= len;
ret += len;
if (maxsize <= 0 || sg_max == 0)
break;
}
rcu_read_unlock();
if (ret > 0)
iov_iter_advance(iter, ret);
return ret;
}
/**
* extract_iter_to_sg - Extract pages from an iterator and add to an sglist
* @iter: The iterator to extract from
* @maxsize: The amount of iterator to copy
* @sgtable: The scatterlist table to fill in
* @sg_max: Maximum number of elements in @sgtable that may be filled
* @extraction_flags: Flags to qualify the request
*
* Extract the page fragments from the given amount of the source iterator and
* add them to a scatterlist that refers to all of those bits, to a maximum
* addition of @sg_max elements.
*
* The pages referred to by UBUF- and IOVEC-type iterators are extracted and
* pinned; BVEC-, KVEC-, FOLIOQ- and XARRAY-type are extracted but aren't
* pinned; DISCARD-type is not supported.
*
* No end mark is placed on the scatterlist; that's left to the caller.
*
* @extraction_flags can have ITER_ALLOW_P2PDMA set to request peer-to-peer DMA
* be allowed on the pages extracted.
*
* If successful, @sgtable->nents is updated to include the number of elements
* added and the number of bytes added is returned. @sgtable->orig_nents is
* left unaltered.
*
* The iov_iter_extract_mode() function should be used to query how cleanup
* should be performed.
*/
ssize_t extract_iter_to_sg(struct iov_iter *iter, size_t maxsize,
struct sg_table *sgtable, unsigned int sg_max,
iov_iter_extraction_t extraction_flags)
{
if (maxsize == 0)
return 0;
switch (iov_iter_type(iter)) {
case ITER_UBUF:
case ITER_IOVEC:
return extract_user_to_sg(iter, maxsize, sgtable, sg_max,
extraction_flags);
case ITER_BVEC:
return extract_bvec_to_sg(iter, maxsize, sgtable, sg_max,
extraction_flags);
case ITER_KVEC:
return extract_kvec_to_sg(iter, maxsize, sgtable, sg_max,
extraction_flags);
case ITER_FOLIOQ:
return extract_folioq_to_sg(iter, maxsize, sgtable, sg_max,
extraction_flags);
case ITER_XARRAY:
return extract_xarray_to_sg(iter, maxsize, sgtable, sg_max,
extraction_flags);
default:
pr_err("%s(%u) unsupported\n", __func__, iov_iter_type(iter));
WARN_ON_ONCE(1);
return -EIO;
}
}
EXPORT_SYMBOL_GPL(extract_iter_to_sg);
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