/* * Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com> * * Scatterlist handling helpers. * * This source code is licensed under the GNU General Public License, * Version 2. See the file COPYING for more details. */ #include <linux/export.h> #include <linux/slab.h> #include <linux/scatterlist.h> #include <linux/highmem.h> #include <linux/kmemleak.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 acount * 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 acount 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 * @skip_first_chunk: don't free the (preallocated) first scatterlist chunk * @free_fn: Free function * * 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, bool skip_first_chunk, sg_free_fn *free_fn) { struct scatterlist *sgl, *next; if (unlikely(!table->sgl)) return; sgl = table->sgl; while (table->orig_nents) { unsigned int alloc_size = table->orig_nents; 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 > max_ents) { next = sg_chain_ptr(&sgl[max_ents - 1]); alloc_size = max_ents; sg_size = alloc_size - 1; } else { sg_size = alloc_size; next = NULL; } table->orig_nents -= sg_size; if (skip_first_chunk) skip_first_chunk = false; else free_fn(sgl, alloc_size); sgl = next; } table->sgl = NULL; } EXPORT_SYMBOL(__sg_free_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, false, sg_kfree); } 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 * @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, gfp_t gfp_mask, sg_alloc_fn *alloc_fn) { struct scatterlist *sg, *prv; unsigned int left; memset(table, 0, sizeof(*table)); if (nents == 0) return -EINVAL; #ifndef CONFIG_ARCH_HAS_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 > max_ents) { alloc_size = 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, 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; } 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, gfp_mask, sg_kmalloc); if (unlikely(ret)) __sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree); return ret; } EXPORT_SYMBOL(sg_alloc_table); /** * __sg_alloc_table_from_pages - Allocate and initialize an sg table from * an array of pages * @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 node in bytes (page aligned) * @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. An 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(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) { unsigned int chunks, cur_page, seg_len, i; int ret; struct scatterlist *s; if (WARN_ON(!max_segment || offset_in_page(max_segment))) return -EINVAL; /* 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 || page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1) { chunks++; seg_len = 0; } } ret = sg_alloc_table(sgt, chunks, gfp_mask); if (unlikely(ret)) return ret; /* merging chunks and putting them into the scatterlist */ cur_page = 0; for_each_sg(sgt->sgl, s, sgt->orig_nents, 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 || page_to_pfn(pages[j]) != page_to_pfn(pages[j - 1]) + 1) break; } chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset; sg_set_page(s, pages[cur_page], min_t(unsigned long, size, chunk_size), offset); size -= chunk_size; offset = 0; cur_page = j; } return 0; } EXPORT_SYMBOL(__sg_alloc_table_from_pages); /** * sg_alloc_table_from_pages - Allocate and initialize an sg table from * an array of pages * @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) * @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. 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(struct sg_table *sgt, struct page **pages, unsigned int n_pages, unsigned int offset, unsigned long size, gfp_t gfp_mask) { return __sg_alloc_table_from_pages(sgt, pages, n_pages, offset, size, SCATTERLIST_MAX_SEGMENT, gfp_mask); } EXPORT_SYMBOL(sg_alloc_table_from_pages); #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) | __GFP_ZERO); 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(sgl); 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); /** * 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 * * 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; unsigned long pgoffset; if (!__sg_page_iter_next(&miter->piter)) return false; sg = miter->piter.sg; pgoffset = miter->piter.sg_pgoffset; miter->__offset = pgoffset ? 0 : sg->offset; miter->__remaining = sg->offset + sg->length - (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 if @miter is stopped, or not proceeded yet. * Otherwise, preemption disabled if the SG_MITER_ATOMIC is set. * * 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: * Preemption disabled if SG_MITER_ATOMIC. Preemption must stay disabled * till @miter is stopped. 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: * Preemption disabled if the SG_MITER_ATOMIC is set. 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) && !PageSlab(miter->page)) flush_kernel_dcache_page(miter->page); if (miter->__flags & SG_MITER_ATOMIC) { WARN_ON_ONCE(preemptible()); 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 false; 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);