new privimitive: iov_iter_revert()
commit 27c0e3748e
upstream.
opposite to iov_iter_advance(); the caller is responsible for never
using it to move back past the initial position.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
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@ -39,7 +39,10 @@ struct iov_iter {
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};
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union {
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unsigned long nr_segs;
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int idx;
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struct {
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int idx;
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int start_idx;
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};
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};
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};
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@ -81,6 +84,7 @@ unsigned long iov_shorten(struct iovec *iov, unsigned long nr_segs, size_t to);
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size_t iov_iter_copy_from_user_atomic(struct page *page,
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struct iov_iter *i, unsigned long offset, size_t bytes);
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void iov_iter_advance(struct iov_iter *i, size_t bytes);
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void iov_iter_revert(struct iov_iter *i, size_t bytes);
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int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes);
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size_t iov_iter_single_seg_count(const struct iov_iter *i);
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size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
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@ -734,6 +734,68 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
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}
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EXPORT_SYMBOL(iov_iter_advance);
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void iov_iter_revert(struct iov_iter *i, size_t unroll)
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{
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if (!unroll)
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return;
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i->count += unroll;
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if (unlikely(i->type & ITER_PIPE)) {
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struct pipe_inode_info *pipe = i->pipe;
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int idx = i->idx;
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size_t off = i->iov_offset;
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while (1) {
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size_t n = off - pipe->bufs[idx].offset;
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if (unroll < n) {
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off -= (n - unroll);
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break;
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}
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unroll -= n;
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if (!unroll && idx == i->start_idx) {
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off = 0;
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break;
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}
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if (!idx--)
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idx = pipe->buffers - 1;
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off = pipe->bufs[idx].offset + pipe->bufs[idx].len;
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}
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i->iov_offset = off;
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i->idx = idx;
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pipe_truncate(i);
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return;
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}
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if (unroll <= i->iov_offset) {
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i->iov_offset -= unroll;
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return;
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}
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unroll -= i->iov_offset;
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if (i->type & ITER_BVEC) {
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const struct bio_vec *bvec = i->bvec;
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while (1) {
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size_t n = (--bvec)->bv_len;
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i->nr_segs++;
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if (unroll <= n) {
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i->bvec = bvec;
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i->iov_offset = n - unroll;
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return;
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}
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unroll -= n;
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}
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} else { /* same logics for iovec and kvec */
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const struct iovec *iov = i->iov;
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while (1) {
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size_t n = (--iov)->iov_len;
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i->nr_segs++;
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if (unroll <= n) {
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i->iov = iov;
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i->iov_offset = n - unroll;
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return;
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}
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unroll -= n;
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}
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}
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}
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EXPORT_SYMBOL(iov_iter_revert);
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/*
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* Return the count of just the current iov_iter segment.
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*/
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@ -787,6 +849,7 @@ void iov_iter_pipe(struct iov_iter *i, int direction,
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i->idx = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);
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i->iov_offset = 0;
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i->count = count;
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i->start_idx = i->idx;
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}
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EXPORT_SYMBOL(iov_iter_pipe);
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