From 3d671ca62a08114810321a2a5e9d3523de5fb1b4 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sun, 25 Apr 2021 09:14:44 -0400 Subject: [PATCH] get rid of iterate_all_kinds() in iov_iter_get_pages()/iov_iter_get_pages_alloc() Here iterate_all_kinds() is used just to find the first (non-empty, in case of iovec) segment. Which can be easily done explicitly. Note that in bvec case we now can get more than PAGE_SIZE worth of them, in case when we have a compound page in bvec and a range that crosses a subpage boundary. Older behaviour had been to stop on that boundary; we used to get the right first page (for_each_bvec() took care of that), but that was all we'd got. Signed-off-by: Al Viro --- lib/iov_iter.c | 147 ++++++++++++++++++++++++++++++------------------- 1 file changed, 91 insertions(+), 56 deletions(-) diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 6569e3f5d01d..3fd331b3b8f2 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -1450,9 +1450,6 @@ static ssize_t pipe_get_pages(struct iov_iter *i, unsigned int iter_head, npages; size_t capacity; - if (!maxsize) - return 0; - if (!sanity(i)) return -EFAULT; @@ -1533,29 +1530,67 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i, return actual; } +/* must be done on non-empty ITER_IOVEC one */ +static unsigned long first_iovec_segment(const struct iov_iter *i, + size_t *size, size_t *start, + size_t maxsize, unsigned maxpages) +{ + size_t skip; + long k; + + for (k = 0, skip = i->iov_offset; k < i->nr_segs; k++, skip = 0) { + unsigned long addr = (unsigned long)i->iov[k].iov_base + skip; + size_t len = i->iov[k].iov_len - skip; + + if (unlikely(!len)) + continue; + if (len > maxsize) + len = maxsize; + len += (*start = addr % PAGE_SIZE); + if (len > maxpages * PAGE_SIZE) + len = maxpages * PAGE_SIZE; + *size = len; + return addr & PAGE_MASK; + } + BUG(); // if it had been empty, we wouldn't get called +} + +/* must be done on non-empty ITER_BVEC one */ +static struct page *first_bvec_segment(const struct iov_iter *i, + size_t *size, size_t *start, + size_t maxsize, unsigned maxpages) +{ + struct page *page; + size_t skip = i->iov_offset, len; + + len = i->bvec->bv_len - skip; + if (len > maxsize) + len = maxsize; + skip += i->bvec->bv_offset; + page = i->bvec->bv_page + skip / PAGE_SIZE; + len += (*start = skip % PAGE_SIZE); + if (len > maxpages * PAGE_SIZE) + len = maxpages * PAGE_SIZE; + *size = len; + return page; +} + ssize_t iov_iter_get_pages(struct iov_iter *i, struct page **pages, size_t maxsize, unsigned maxpages, size_t *start) { + size_t len; + int n, res; + if (maxsize > i->count) maxsize = i->count; + if (!maxsize) + return 0; - if (unlikely(iov_iter_is_pipe(i))) - return pipe_get_pages(i, pages, maxsize, maxpages, start); - if (unlikely(iov_iter_is_xarray(i))) - return iter_xarray_get_pages(i, pages, maxsize, maxpages, start); - if (unlikely(iov_iter_is_discard(i))) - return -EFAULT; + if (likely(iter_is_iovec(i))) { + unsigned long addr; - iterate_all_kinds(i, maxsize, v, ({ - unsigned long addr = (unsigned long)v.iov_base; - size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1)); - int n; - int res; - - if (len > maxpages * PAGE_SIZE) - len = maxpages * PAGE_SIZE; - addr &= ~(PAGE_SIZE - 1); + addr = first_iovec_segment(i, &len, start, maxsize, maxpages); n = DIV_ROUND_UP(len, PAGE_SIZE); res = get_user_pages_fast(addr, n, iov_iter_rw(i) != WRITE ? FOLL_WRITE : 0, @@ -1563,17 +1598,21 @@ ssize_t iov_iter_get_pages(struct iov_iter *i, if (unlikely(res < 0)) return res; return (res == n ? len : res * PAGE_SIZE) - *start; - 0;}),({ - /* can't be more than PAGE_SIZE */ - *start = v.bv_offset; - get_page(*pages = v.bv_page); - return v.bv_len; - }),({ - return -EFAULT; - }), - 0 - ) - return 0; + } + if (iov_iter_is_bvec(i)) { + struct page *page; + + page = first_bvec_segment(i, &len, start, maxsize, maxpages); + n = DIV_ROUND_UP(len, PAGE_SIZE); + while (n--) + get_page(*pages++ = page++); + return len - *start; + } + if (iov_iter_is_pipe(i)) + return pipe_get_pages(i, pages, maxsize, maxpages, start); + if (iov_iter_is_xarray(i)) + return iter_xarray_get_pages(i, pages, maxsize, maxpages, start); + return -EFAULT; } EXPORT_SYMBOL(iov_iter_get_pages); @@ -1590,9 +1629,6 @@ static ssize_t pipe_get_pages_alloc(struct iov_iter *i, unsigned int iter_head, npages; ssize_t n; - if (!maxsize) - return 0; - if (!sanity(i)) return -EFAULT; @@ -1665,24 +1701,18 @@ ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, size_t *start) { struct page **p; + size_t len; + int n, res; if (maxsize > i->count) maxsize = i->count; + if (!maxsize) + return 0; - if (unlikely(iov_iter_is_pipe(i))) - return pipe_get_pages_alloc(i, pages, maxsize, start); - if (unlikely(iov_iter_is_xarray(i))) - return iter_xarray_get_pages_alloc(i, pages, maxsize, start); - if (unlikely(iov_iter_is_discard(i))) - return -EFAULT; + if (likely(iter_is_iovec(i))) { + unsigned long addr; - iterate_all_kinds(i, maxsize, v, ({ - unsigned long addr = (unsigned long)v.iov_base; - size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1)); - int n; - int res; - - addr &= ~(PAGE_SIZE - 1); + addr = first_iovec_segment(i, &len, start, maxsize, ~0U); n = DIV_ROUND_UP(len, PAGE_SIZE); p = get_pages_array(n); if (!p) @@ -1695,19 +1725,24 @@ ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, } *pages = p; return (res == n ? len : res * PAGE_SIZE) - *start; - 0;}),({ - /* can't be more than PAGE_SIZE */ - *start = v.bv_offset; - *pages = p = get_pages_array(1); + } + if (iov_iter_is_bvec(i)) { + struct page *page; + + page = first_bvec_segment(i, &len, start, maxsize, ~0U); + n = DIV_ROUND_UP(len, PAGE_SIZE); + *pages = p = get_pages_array(n); if (!p) return -ENOMEM; - get_page(*p = v.bv_page); - return v.bv_len; - }),({ - return -EFAULT; - }), 0 - ) - return 0; + while (n--) + get_page(*p++ = page++); + return len - *start; + } + if (iov_iter_is_pipe(i)) + return pipe_get_pages_alloc(i, pages, maxsize, start); + if (iov_iter_is_xarray(i)) + return iter_xarray_get_pages_alloc(i, pages, maxsize, start); + return -EFAULT; } EXPORT_SYMBOL(iov_iter_get_pages_alloc);