提交 27c0e374 编写于 作者: A Al Viro

[iov_iter] new privimitive: iov_iter_revert()

opposite to iov_iter_advance(); the caller is responsible for never
using it to move back past the initial position.

Cc: stable@vger.kernel.org
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
上级 c02ed2e7
master alk-4.19.24 alk-4.19.30 alk-4.19.34 alk-4.19.36 alk-4.19.43 alk-4.19.48 alk-4.19.57 ck-4.19.67 ck-4.19.81 ck-4.19.91 github/fork/deepanshu1422/fix-typo-in-comment github/fork/haosdent/fix-typo linux-next v4.19.91 v4.19.90 v4.19.89 v4.19.88 v4.19.87 v4.19.86 v4.19.85 v4.19.84 v4.19.83 v4.19.82 v4.19.81 v4.19.80 v4.19.79 v4.19.78 v4.19.77 v4.19.76 v4.19.75 v4.19.74 v4.19.73 v4.19.72 v4.19.71 v4.19.70 v4.19.69 v4.19.68 v4.19.67 v4.19.66 v4.19.65 v4.19.64 v4.19.63 v4.19.62 v4.19.61 v4.19.60 v4.19.59 v4.19.58 v4.19.57 v4.19.56 v4.19.55 v4.19.54 v4.19.53 v4.19.52 v4.19.51 v4.19.50 v4.19.49 v4.19.48 v4.19.47 v4.19.46 v4.19.45 v4.19.44 v4.19.43 v4.19.42 v4.19.41 v4.19.40 v4.19.39 v4.19.38 v4.19.37 v4.19.36 v4.19.35 v4.19.34 v4.19.33 v4.19.32 v4.19.31 v4.19.30 v4.19.29 v4.19.28 v4.19.27 v4.19.26 v4.19.25 v4.19.24 v4.19.23 v4.19.22 v4.19.21 v4.19.20 v4.19.19 v4.19.18 v4.19.17 v4.19.16 v4.19.15 v4.19.14 v4.19.13 v4.19.12 v4.19.11 v4.19.10 v4.19.9 v4.19.8 v4.19.7 v4.19.6 v4.19.5 v4.19.4 v4.19.3 v4.19.2 v4.19.1 v4.19 v4.19-rc8 v4.19-rc7 v4.19-rc6 v4.19-rc5 v4.19-rc4 v4.19-rc3 v4.19-rc2 v4.19-rc1 ck-release-21 ck-release-20 ck-release-19.2 ck-release-19.1 ck-release-19 ck-release-18 ck-release-17.2 ck-release-17.1 ck-release-17 ck-release-16 ck-release-15.1 ck-release-15 ck-release-14 ck-release-13.2 ck-release-13 ck-release-12 ck-release-11 ck-release-10 ck-release-9 ck-release-7 alk-release-15 alk-release-14 alk-release-13.2 alk-release-13 alk-release-12 alk-release-11 alk-release-10 alk-release-9 alk-release-7
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......@@ -39,7 +39,10 @@ struct iov_iter {
};
union {
unsigned long nr_segs;
int idx;
struct {
int idx;
int start_idx;
};
};
};
......@@ -81,6 +84,7 @@ unsigned long iov_shorten(struct iovec *iov, unsigned long nr_segs, size_t to);
size_t iov_iter_copy_from_user_atomic(struct page *page,
struct iov_iter *i, unsigned long offset, size_t bytes);
void iov_iter_advance(struct iov_iter *i, size_t bytes);
void iov_iter_revert(struct iov_iter *i, size_t bytes);
int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes);
size_t iov_iter_single_seg_count(const struct iov_iter *i);
size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
......
......@@ -786,6 +786,68 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
}
EXPORT_SYMBOL(iov_iter_advance);
void iov_iter_revert(struct iov_iter *i, size_t unroll)
{
if (!unroll)
return;
i->count += unroll;
if (unlikely(i->type & ITER_PIPE)) {
struct pipe_inode_info *pipe = i->pipe;
int idx = i->idx;
size_t off = i->iov_offset;
while (1) {
size_t n = off - pipe->bufs[idx].offset;
if (unroll < n) {
off -= (n - unroll);
break;
}
unroll -= n;
if (!unroll && idx == i->start_idx) {
off = 0;
break;
}
if (!idx--)
idx = pipe->buffers - 1;
off = pipe->bufs[idx].offset + pipe->bufs[idx].len;
}
i->iov_offset = off;
i->idx = idx;
pipe_truncate(i);
return;
}
if (unroll <= i->iov_offset) {
i->iov_offset -= unroll;
return;
}
unroll -= i->iov_offset;
if (i->type & ITER_BVEC) {
const struct bio_vec *bvec = i->bvec;
while (1) {
size_t n = (--bvec)->bv_len;
i->nr_segs++;
if (unroll <= n) {
i->bvec = bvec;
i->iov_offset = n - unroll;
return;
}
unroll -= n;
}
} else { /* same logics for iovec and kvec */
const struct iovec *iov = i->iov;
while (1) {
size_t n = (--iov)->iov_len;
i->nr_segs++;
if (unroll <= n) {
i->iov = iov;
i->iov_offset = n - unroll;
return;
}
unroll -= n;
}
}
}
EXPORT_SYMBOL(iov_iter_revert);
/*
* Return the count of just the current iov_iter segment.
*/
......@@ -839,6 +901,7 @@ void iov_iter_pipe(struct iov_iter *i, int direction,
i->idx = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);
i->iov_offset = 0;
i->count = count;
i->start_idx = i->idx;
}
EXPORT_SYMBOL(iov_iter_pipe);
......
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