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Fri, 21 Mar 2025 16:14:29 +0000 (UTC) Received: from warthog.procyon.org.com (unknown [10.42.28.61]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 075461955BFE; Fri, 21 Mar 2025 16:14:25 +0000 (UTC) From: David Howells To: Leon Romanovsky Cc: David Howells , Christian Brauner , Matthew Wilcox , Chuck Lever , Steve French , Ilya Dryomov , netfs@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [RFC PATCH 3/4] iov_iter: Add a scatterlist iterator type Date: Fri, 21 Mar 2025 16:14:03 +0000 Message-ID: <20250321161407.3333724-4-dhowells@redhat.com> In-Reply-To: <20250321161407.3333724-1-dhowells@redhat.com> References: <20250321161407.3333724-1-dhowells@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 X-Rspamd-Queue-Id: A4ACF100017 X-Stat-Signature: 5z7kf4xbjitdsdcfutkg5xffx4ri59i4 X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1742573675-391205 X-HE-Meta: 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 woVGfZxZ iN12bTFfVyYQw+cA6W0C90CsnLSBnaMpTZy4pe3Yu3l2oR5i6g1D+crs6+LULbsomvYwN/duB3ZOatrblDSOgJSP8W0tJ1dSccalwXqeIE5i/gLmSCZ96yJj+MadpTOH6mpwOh/F256FXuJgINFFbzMhXwBpSS2n4WO5e94UuxP+OJfK4yOqvS+Khb86YNViUXJbyBnYjwMJSFosDTLYIBxSN8XTDWVsh09ymKj8R7uWQWitzn/Z4I04i6W8YnoiOpT/vv2Jyz9eqmZ/KKG2Ixdv2XnD2kygZqH2okJcuifQ86NzdK3sqvIZViCtAe49Pz95cIkHmBGz+7lBBlTugNjB99lZg9xd0OWh0ritNVkANyKDRui73b7/C2cXCqE2dPwJ0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Add an iterator type that can iterate over a scatterlist. This can be used as a bridge to help convert things that take scatterlists into things that take I/O iterators. Signed-off-by: David Howells --- include/linux/uio.h | 12 ++ lib/iov_iter.c | 315 +++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 321 insertions(+), 6 deletions(-) diff --git a/include/linux/uio.h b/include/linux/uio.h index 59a586333e1b..0e50f4af6877 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -12,6 +12,7 @@ struct page; struct folio_queue; +struct scatterlist; typedef unsigned int __bitwise iov_iter_extraction_t; @@ -30,6 +31,7 @@ enum iter_type { ITER_XARRAY, ITER_DISCARD, ITER_ITERLIST, + ITER_SCATTERLIST, }; #define ITER_SOURCE 1 // == WRITE @@ -46,6 +48,7 @@ struct iov_iter { bool nofault; bool data_source; size_t iov_offset; + size_t orig_count; /* * Hack alert: overlay ubuf_iovec with iovec + count, so * that the members resolve correctly regardless of the type @@ -73,11 +76,13 @@ struct iov_iter { struct xarray *xarray; void __user *ubuf; struct iov_iterlist *iterlist; + struct scatterlist *sglist; }; size_t count; }; }; union { + struct scatterlist *sglist_head; unsigned long nr_segs; u8 folioq_slot; loff_t xarray_start; @@ -161,6 +166,11 @@ static inline bool iov_iter_is_iterlist(const struct iov_iter *i) return iov_iter_type(i) == ITER_ITERLIST; } +static inline bool iov_iter_is_scatterlist(const struct iov_iter *i) +{ + return iov_iter_type(i) == ITER_SCATTERLIST; +} + static inline unsigned char iov_iter_rw(const struct iov_iter *i) { return i->data_source ? WRITE : READ; @@ -317,6 +327,8 @@ void iov_iter_xarray(struct iov_iter *i, unsigned int direction, struct xarray * void iov_iter_iterlist(struct iov_iter *i, unsigned int direction, struct iov_iterlist *iterlist, unsigned long nr_segs, size_t count); +void iov_iter_scatterlist(struct iov_iter *i, unsigned int direction, + struct scatterlist *sglist, size_t count); ssize_t iov_iter_get_pages2(struct iov_iter *i, struct page **pages, size_t maxsize, unsigned maxpages, size_t *start); ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i, struct page ***pages, diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 1d9190abfeb5..ed9859af3c5d 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -562,6 +562,26 @@ static void iov_iter_folioq_advance(struct iov_iter *i, size_t size) i->folioq = folioq; } +static void iov_iter_scatterlist_advance(struct iov_iter *i, size_t size) +{ + struct scatterlist *sg; + + if (!i->count) + return; + i->count -= size; + + size += i->iov_offset; + + for (sg = i->sglist; sg; sg_next(sg)) { + if (likely(size < sg->length)) + break; + size -= sg->length; + } + WARN_ON(!sg && size > 0); + i->iov_offset = size; + i->sglist = sg; +} + void iov_iter_advance(struct iov_iter *i, size_t size) { if (unlikely(i->count < size)) @@ -591,6 +611,8 @@ void iov_iter_advance(struct iov_iter *i, size_t size) i->iterlist++; i->nr_segs--; } + } else if (iov_iter_is_scatterlist(i)) { + iov_iter_scatterlist_advance(i, size); } } EXPORT_SYMBOL(iov_iter_advance); @@ -638,6 +660,15 @@ static void iov_iter_revert_iterlist(struct iov_iter *i, size_t unroll) } } +static void iov_iter_revert_scatterlist(struct iov_iter *i) +{ + size_t skip = i->orig_count - i->count; + + i->sglist = i->sglist_head; + i->count = i->orig_count; + iov_iter_advance(i, skip); +} + void iov_iter_revert(struct iov_iter *i, size_t unroll) { if (!unroll) @@ -649,6 +680,8 @@ void iov_iter_revert(struct iov_iter *i, size_t unroll) return; if (unlikely(iov_iter_is_iterlist(i))) return iov_iter_revert_iterlist(i, unroll); + if (unlikely(iov_iter_is_scatterlist(i))) + return iov_iter_revert_scatterlist(i); if (unroll <= i->iov_offset) { i->iov_offset -= unroll; return; @@ -706,6 +739,8 @@ size_t iov_iter_single_seg_count(const struct iov_iter *i) if (unlikely(iov_iter_is_folioq(i))) return !i->count ? 0 : umin(folioq_folio_size(i->folioq, i->folioq_slot), i->count); + if (unlikely(iov_iter_is_scatterlist(i))) + return !i->sglist ? 0 : umin(i->count, i->sglist->length - i->iov_offset); return i->count; } EXPORT_SYMBOL(iov_iter_single_seg_count); @@ -856,6 +891,33 @@ void iov_iter_iterlist(struct iov_iter *iter, unsigned int direction, } EXPORT_SYMBOL(iov_iter_iterlist); +/** + * iov_iter_scatterlist - Initialise an I/O iterator for a scatterlist chain + * @iter: The iterator to initialise. + * @direction: The direction of the transfer. + * @sglist: The head of the scatterlist + * @count: The size of the I/O buffer in bytes. + * + * Set up an I/O iterator that walks over a scatterlist. Because scatterlists + * can be chained and have no back pointers, reversion requires starting again + * at the beginning and counting forwards. + */ +void iov_iter_scatterlist(struct iov_iter *iter, unsigned int direction, + struct scatterlist *sglist, size_t count) +{ + WARN_ON(direction & ~(READ | WRITE)); + *iter = (struct iov_iter){ + .iter_type = ITER_SCATTERLIST, + .data_source = direction, + .sglist = sglist, + .sglist_head = sglist, + .iov_offset = 0, + .count = count, + .orig_count = count, + }; +} +EXPORT_SYMBOL(iov_iter_scatterlist); + static bool iov_iter_aligned_iovec(const struct iov_iter *i, unsigned addr_mask, unsigned len_mask) { @@ -994,6 +1056,26 @@ static unsigned long iov_iter_alignment_bvec(const struct iov_iter *i) return res; } +static unsigned long iov_iter_alignment_scatterlist(const struct iov_iter *i) +{ + struct scatterlist *sg; + unsigned skip = i->iov_offset; + unsigned res = 0; + size_t size = i->count; + + for (sg = i->sglist; sg; sg = sg_next(sg)) { + size_t len = sg->length - skip; + res |= (unsigned long)sg->offset + skip; + if (len > size) + len = size; + res |= len; + size -= len; + skip = 0; + } while (size); + + return res; +} + unsigned long iov_iter_alignment(const struct iov_iter *i) { if (likely(iter_is_ubuf(i))) { @@ -1024,6 +1106,8 @@ unsigned long iov_iter_alignment(const struct iov_iter *i) align |= iov_iter_alignment(&i->iterlist[j].iter); return align; } + if (iov_iter_is_scatterlist(i)) + return iov_iter_alignment_scatterlist(i); return 0; } @@ -1058,13 +1142,8 @@ unsigned long iov_iter_gap_alignment(const struct iov_iter *i) } EXPORT_SYMBOL(iov_iter_gap_alignment); -static int want_pages_array(struct page ***res, size_t size, - size_t start, unsigned int maxpages) +static int __want_pages_array(struct page ***res, unsigned int count) { - unsigned int count = DIV_ROUND_UP(size + start, PAGE_SIZE); - - if (count > maxpages) - count = maxpages; WARN_ON(!count); // caller should've prevented that if (!*res) { *res = kvmalloc_array(count, sizeof(struct page *), GFP_KERNEL); @@ -1074,6 +1153,16 @@ static int want_pages_array(struct page ***res, size_t size, return count; } +static int want_pages_array(struct page ***res, size_t size, + size_t start, unsigned int maxpages) +{ + size_t count = DIV_ROUND_UP(size + start, PAGE_SIZE); + + if (count > maxpages) + count = maxpages; + return __want_pages_array(res, count); +} + static ssize_t iter_folioq_get_pages(struct iov_iter *iter, struct page ***ppages, size_t maxsize, unsigned maxpages, size_t *_start_offset) @@ -1186,6 +1275,52 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i, return maxsize; } +static struct page *first_scatterlist_segment(const struct iov_iter *i, + size_t *size, size_t *start) +{ + struct scatterlist *sg = i->sglist; + struct page *page; + size_t skip = i->iov_offset, len; + + if (!sg) + return NULL; + + len = sg->length - skip; + if (*size > len) + *size = len; + skip += sg->offset; + page = sg_page(sg) + skip / PAGE_SIZE; + *start = skip % PAGE_SIZE; + return page; +} + +static ssize_t iter_scatterlist_get_pages(struct iov_iter *i, + struct page ***pages, size_t maxsize, + unsigned maxpages, size_t *start) +{ + struct page **p, *page; + unsigned int n; + + page = first_scatterlist_segment(i, &maxsize, start); + if (!page) + return -EFAULT; + n = want_pages_array(pages, maxsize, *start, maxpages); + if (!n) + return -ENOMEM; + p = *pages; + for (int k = 0; k < n; k++) + get_page(p[k] = page + k); + maxsize = min_t(size_t, maxsize, n * PAGE_SIZE - *start); + i->count -= maxsize; + i->iov_offset += maxsize; + if (i->iov_offset == i->bvec->bv_len) { + i->iov_offset = 0; + i->bvec++; + i->nr_segs--; + } + return maxsize; +} + /* must be done on non-empty ITER_UBUF or ITER_IOVEC one */ static unsigned long first_iovec_segment(const struct iov_iter *i, size_t *size) { @@ -1296,6 +1431,8 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i, i->count -= size; return size; } + if (iov_iter_is_scatterlist(i)) + return iter_scatterlist_get_pages(i, pages, maxsize, maxpages, start); return -EFAULT; } @@ -1379,6 +1516,25 @@ static int iterlist_npages(const struct iov_iter *i, int maxpages) return npages; } +static int scatterlist_npages(const struct iov_iter *i, int maxpages) +{ + struct scatterlist *sg; + size_t skip = i->iov_offset, size = i->count; + int npages = 0; + + for (sg = i->sglist; sg && size; sg = sg_next(sg)) { + unsigned offs = (sg->offset + skip) % PAGE_SIZE; + size_t len = umin(sg->length - skip, size); + + size -= len; + npages += DIV_ROUND_UP(offs + len, PAGE_SIZE); + if (unlikely(npages > maxpages)) + return maxpages; + skip = 0; + } + return npages; +} + int iov_iter_npages(const struct iov_iter *i, int maxpages) { if (unlikely(!i->count)) @@ -1405,6 +1561,8 @@ int iov_iter_npages(const struct iov_iter *i, int maxpages) } if (iov_iter_is_iterlist(i)) return iterlist_npages(i, maxpages); + if (iov_iter_is_scatterlist(i)) + return scatterlist_npages(i, maxpages); return 0; } EXPORT_SYMBOL(iov_iter_npages); @@ -1792,6 +1950,107 @@ static ssize_t iov_iter_extract_xarray_pages(struct iov_iter *i, return maxsize; } +/* + * Count the number of virtually contiguous pages in a scatterlist iterator + * from the current point. + */ +static size_t count_scatterlist_contig_pages(const struct iov_iter *i, + size_t maxpages, size_t maxsize) +{ + struct scatterlist *sg; + size_t npages = 0; + size_t skip = i->iov_offset, size = umin(i->count, maxsize); + + for (sg = i->sglist; sg && size; sg = sg_next(sg)) { + size_t offs = (sg->offset + skip) % PAGE_SIZE; + size_t part = umin(sg->length - skip, size); + + if (!part) + break; + size -= part; + npages += DIV_ROUND_UP(offs + part, PAGE_SIZE); + if (unlikely(npages > maxpages)) + return maxpages; + if (((offs + part) % PAGE_SIZE) != 0) + break; + skip = 0; + } + return npages; +} + +/* + * Extract a list of contiguous pages from an ITER_FOLIOQ iterator. This does + * not get references on the pages, nor does it get a pin on them. + */ +static ssize_t iov_iter_extract_scatterlist_pages(struct iov_iter *i, + struct page ***pages, size_t maxsize, + unsigned int maxpages, + iov_iter_extraction_t extraction_flags, + size_t *offset0) +{ + struct scatterlist *sg = i->sglist; + struct page **p; + size_t npages, skip, size = 0; + int nr = 0; + + if (!sg) + return 0; + + while (skip = i->iov_offset, + skip == sg->length) { + sg = sg_next(sg); + i->sglist = sg; + i->iov_offset = 0; + if (!sg) + return 0; + } + + npages = count_scatterlist_contig_pages(i, maxpages, maxsize); + + maxpages = __want_pages_array(pages, npages); + if (!maxpages) + return -ENOMEM; + *offset0 = (sg->offset + skip) & ~PAGE_MASK; + p = *pages; + + for (sg = i->sglist; sg; sg = sg_next(sg)) { + struct page *page = sg_page(sg); + size_t part = umin(sg->length - skip, maxsize); + size_t off = sg->offset + skip; + + if (!part) + break; + + page += off / PAGE_SIZE; + off %= PAGE_SIZE; + + do { + size_t chunk = umin(part, PAGE_SIZE - off); + + p[nr++] = page; + page++; + maxpages--; + maxsize -= chunk; + size += chunk; + skip += chunk; + part -= chunk; + off = 0; + } while (part && maxsize && maxpages); + + if (((sg->offset + skip + part) % PAGE_SIZE) != 0) + break; + if (!maxsize || !maxpages) { + if (!part) + sg = sg_next(sg); + break; + } + skip = 0; + } + + iov_iter_advance(i, size); + return size; +} + /* * Extract a list of virtually contiguous pages from an ITER_BVEC iterator. * This does not get references on the pages, nor does it get a pin on them. @@ -2051,6 +2310,10 @@ ssize_t iov_iter_extract_pages(struct iov_iter *i, i->count -= size; return size; } + if (iov_iter_is_scatterlist(i)) + return iov_iter_extract_scatterlist_pages(i, pages, maxsize, + maxpages, extraction_flags, + offset0); return -EFAULT; } EXPORT_SYMBOL_GPL(iov_iter_extract_pages); @@ -2148,6 +2411,44 @@ static size_t iterate_iterlist(struct iov_iter *iter, size_t len, void *priv, vo return progress; } +/* + * Handle iteration over ITER_SCATTERLIST. + */ +static size_t iterate_scatterlist(struct iov_iter *iter, size_t len, void *priv, void *priv2, + iov_step_f step) +{ + struct scatterlist *sg = iter->sglist; + size_t progress = 0, skip = iter->iov_offset; + + do { + struct page *page = sg_page(sg); + size_t remain, consumed; + size_t offset = sg->offset + skip, part; + void *kaddr = kmap_local_page(page + offset / PAGE_SIZE); + + part = min3(len, + (size_t)(sg->length - skip), + (size_t)(PAGE_SIZE - offset % PAGE_SIZE)); + remain = step(kaddr + offset % PAGE_SIZE, progress, part, priv, priv2); + kunmap_local(kaddr); + consumed = part - remain; + len -= consumed; + progress += consumed; + skip += consumed; + if (skip >= sg->length) { + skip = 0; + sg = sg_next(sg); + } + if (remain) + break; + } while (len); + + iter->sglist = sg; + iter->iov_offset = skip; + iter->count -= progress; + return progress; +} + /* * Out of line iteration for iterator types that don't need such fast handling. */ @@ -2160,6 +2461,8 @@ size_t __iterate_and_advance2(struct iov_iter *iter, size_t len, void *priv, return iterate_xarray(iter, len, priv, priv2, step); if (iov_iter_is_iterlist(iter)) return iterate_iterlist(iter, len, priv, priv2, ustep, step); + if (iov_iter_is_scatterlist(iter)) + return iterate_scatterlist(iter, len, priv, priv2, step); WARN_ON(1); return 0; }