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iov_iter_npages(): don't bother with iterate_all_kinds() 

note that in bvec case pages can be compound ones - we can't just assume
that each segment is covered by one (sub)page

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2021-04-25 16:00:48 -04:00
parent 3d671ca62a
commit 66531c65aa
1 changed files with 54 additions and 34 deletions
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88
lib/iov_iter.c
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@ -1864,19 +1864,56 @@ size_t hash_and_copy_to_iter(const void *addr, size_t bytes, void *hashp,
}
EXPORT_SYMBOL(hash_and_copy_to_iter);
int iov_iter_npages(const struct iov_iter *i, int maxpages)
static int iov_npages(const struct iov_iter *i, int maxpages)
{
size_t size = i->count;
size_t skip = i->iov_offset, size = i->count;
const struct iovec *p;
int npages = 0;
if (!size)
return 0;
if (unlikely(iov_iter_is_discard(i)))
return 0;
for (p = i->iov; size; skip = 0, p++) {
unsigned offs = offset_in_page(p->iov_base + skip);
size_t len = min(p->iov_len - skip, size);
if (unlikely(iov_iter_is_pipe(i))) {
struct pipe_inode_info *pipe = i->pipe;
if (len) {
size -= len;
npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
if (unlikely(npages > maxpages))
return maxpages;
}
}
return npages;
}
static int bvec_npages(const struct iov_iter *i, int maxpages)
{
size_t skip = i->iov_offset, size = i->count;
const struct bio_vec *p;
int npages = 0;
for (p = i->bvec; size; skip = 0, p++) {
unsigned offs = (p->bv_offset + skip) % PAGE_SIZE;
size_t len = min(p->bv_len - skip, size);
size -= len;
npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
if (unlikely(npages > maxpages))
return maxpages;
}
return npages;
}
int iov_iter_npages(const struct iov_iter *i, int maxpages)
{
if (unlikely(!i->count))
return 0;
/* iovec and kvec have identical layouts */
if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
return iov_npages(i, maxpages);
if (iov_iter_is_bvec(i))
return bvec_npages(i, maxpages);
if (iov_iter_is_pipe(i)) {
unsigned int iter_head;
int npages;
size_t off;
if (!sanity(i))
@ -1884,11 +1921,13 @@ int iov_iter_npages(const struct iov_iter *i, int maxpages)
data_start(i, &iter_head, &off);
/* some of this one + all after this one */
npages = pipe_space_for_user(iter_head, pipe->tail, pipe);
if (npages >= maxpages)
return maxpages;
} else if (unlikely(iov_iter_is_xarray(i))) {
npages = pipe_space_for_user(iter_head, i->pipe->tail, i->pipe);
return min(npages, maxpages);
}
if (iov_iter_is_xarray(i)) {
size_t size = i->count;
unsigned offset;
int npages;
offset = (i->xarray_start + i->iov_offset) & ~PAGE_MASK;
@ -1900,28 +1939,9 @@ int iov_iter_npages(const struct iov_iter *i, int maxpages)
if (size)
npages++;
}
if (npages >= maxpages)
return maxpages;
} else iterate_all_kinds(i, size, v, ({
unsigned long p = (unsigned long)v.iov_base;
npages += DIV_ROUND_UP(p + v.iov_len, PAGE_SIZE)
- p / PAGE_SIZE;
if (npages >= maxpages)
return maxpages;
0;}),({
npages++;
if (npages >= maxpages)
return maxpages;
}),({
unsigned long p = (unsigned long)v.iov_base;
npages += DIV_ROUND_UP(p + v.iov_len, PAGE_SIZE)
- p / PAGE_SIZE;
if (npages >= maxpages)
return maxpages;
}),
0
)
return npages;
return min(npages, maxpages);
}
return 0;
}
EXPORT_SYMBOL(iov_iter_npages);