iov_iter: make the amount already copied available to iterator callbacks

Making iterator macros keep track of the amount of data copied is pretty
easy and it has several benefits:
	1) we no longer need the mess like (from += v.iov_len) - v.iov_len
in the callbacks - initial value + total amount copied so far would do
just fine.
	2) less obviously, we no longer need to remember the initial amount
of data we wanted to copy; the loops in iterator macros are along the lines
of
	wanted = bytes;
	while (bytes) {
		copy some
		bytes -= copied
		if short copy
			break
	}
	bytes = wanted - bytes;
Replacement is
	offs = 0;
	while (bytes) {
		copy some
		offs += copied
		bytes -= copied
		if short copy
			break
	}
	bytes = offs;
That wouldn't be a win per se, but unlike the initial value of bytes, the amount
copied so far *is* useful in callbacks.
	3) in some cases (csum_and_copy_..._iter()) we already had offs manually
maintained by the callbacks.  With that change we can drop that.

	Less boilerplate and more readable code...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 74e20d6d6e3d725aa10ccfb126cb64f3cb1475e2..0e04abe9ec49f1de4f1def899627805c48176844 100644 (file)
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -17,15 +17,14 @@
 #define PIPE_PARANOIA /* for now */
 
 /* covers iovec and kvec alike */
-#define iterate_iovec(i, n, __v, __p, skip, STEP) {            \
-       size_t left;                                            \
-       size_t wanted = n;                                      \
+#define iterate_iovec(i, n, __v, __off, __p, skip, STEP) {     \
+       size_t __off = 0;                                       \
        do {                                                    \
                __v.iov_len = min(n, __p->iov_len - skip);      \
                if (likely(__v.iov_len)) {                      \
                        __v.iov_base = __p->iov_base + skip;    \
-                       left = (STEP);                          \
-                       __v.iov_len -= left;                    \
+                       __v.iov_len -= (STEP);                  \
+                       __off += __v.iov_len;                   \
                        skip += __v.iov_len;                    \
                        n -= __v.iov_len;                       \
                        if (skip < __p->iov_len)                \
@@ -34,11 +33,11 @@
                __p++;                                          \
                skip = 0;                                       \
        } while (n);                                            \
-       n = wanted - n;                                         \
+       n = __off;                                              \
 }
 
-#define iterate_bvec(i, n, __v, p, skip, STEP) {               \
-       size_t wanted = n;                                      \
+#define iterate_bvec(i, n, __v, __off, p, skip, STEP) {                \
+       size_t __off = 0;                                       \
        while (n) {                                             \
                unsigned offset = p->bv_offset + skip;          \
                unsigned left;                                  \
@@ -50,6 +49,7 @@
                left = (STEP);                                  \
                kunmap_local(kaddr);                            \
                __v.iov_len -= left;                            \
+               __off += __v.iov_len;                           \
                skip += __v.iov_len;                            \
                if (skip == p->bv_len) {                        \
                        skip = 0;                               \
@@ -59,13 +59,14 @@
                if (left)                                       \
                        break;                                  \
        }                                                       \
-       n = wanted - n;                                         \
+       n = __off;                                              \
 }
 
-#define iterate_xarray(i, n, __v, skip, STEP) {                \
+#define iterate_xarray(i, n, __v, __off, skip, STEP) {         \
        __label__ __out;                                        \
+       size_t __off = 0;                                       \
        struct page *head = NULL;                               \
-       size_t wanted = n, seg, offset;                         \
+       size_t seg, offset;                                     \
        loff_t start = i->xarray_start + skip;                  \
        pgoff_t index = start >> PAGE_SHIFT;                    \
        int j;                                                  \
@@ -84,25 +85,26 @@
                for (j = (head->index < index) ? index - head->index : 0; \
                     j < thp_nr_pages(head); j++) {                     \
                        void *kaddr = kmap_local_page(head + j);        \
-                       offset = (i->xarray_start + skip) % PAGE_SIZE;  \
+                       offset = (start + __off) % PAGE_SIZE;           \
                        __v.iov_base = kaddr + offset;                  \
                        seg = PAGE_SIZE - offset;                       \
                        __v.iov_len = min(n, seg);                      \
                        left = (STEP);                                  \
                        kunmap_local(kaddr);                            \
                        __v.iov_len -= left;                            \
+                       __off += __v.iov_len;                           \
                        n -= __v.iov_len;                               \
-                       skip += __v.iov_len;                            \
                        if (left || n == 0)                             \
                                goto __out;                             \
                }                                                       \
        }                                                       \
 __out:                                                         \
        rcu_read_unlock();                                      \
-       n = wanted - n;                                         \
+       skip += __off;                                          \
+       n = __off;                                              \
 }
 
-#define __iterate_and_advance(i, n, v, I, K) {                 \
+#define __iterate_and_advance(i, n, v, off, I, K) {            \
        if (unlikely(i->count < n))                             \
                n = i->count;                                   \
        if (likely(n)) {                                        \
@@ -110,31 +112,31 @@ __out:                                                            \
                if (likely(iter_is_iovec(i))) {                 \
                        const struct iovec *iov = i->iov;       \
                        struct iovec v;                         \
-                       iterate_iovec(i, n, v, iov, skip, (I))  \
+                       iterate_iovec(i, n, v, off, iov, skip, (I))     \
                        i->nr_segs -= iov - i->iov;             \
                        i->iov = iov;                           \
                } else if (iov_iter_is_bvec(i)) {               \
                        const struct bio_vec *bvec = i->bvec;   \
                        struct kvec v;                          \
-                       iterate_bvec(i, n, v, bvec, skip, (K))  \
+                       iterate_bvec(i, n, v, off, bvec, skip, (K))     \
                        i->nr_segs -= bvec - i->bvec;           \
                        i->bvec = bvec;                         \
                } else if (iov_iter_is_kvec(i)) {               \
                        const struct kvec *kvec = i->kvec;      \
                        struct kvec v;                          \
-                       iterate_iovec(i, n, v, kvec, skip, (K)) \
+                       iterate_iovec(i, n, v, off, kvec, skip, (K))    \
                        i->nr_segs -= kvec - i->kvec;           \
                        i->kvec = kvec;                         \
                } else if (iov_iter_is_xarray(i)) {             \
                        struct kvec v;                          \
-                       iterate_xarray(i, n, v, skip, (K))      \
+                       iterate_xarray(i, n, v, off, skip, (K)) \
                }                                               \
                i->count -= n;                                  \
                i->iov_offset = skip;                           \
        }                                                       \
 }
-#define iterate_and_advance(i, n, v, I, K) \
-       __iterate_and_advance(i, n, v, I, ((void)(K),0))
+#define iterate_and_advance(i, n, v, off, I, K) \
+       __iterate_and_advance(i, n, v, off, I, ((void)(K),0))
 
 static int copyout(void __user *to, const void *from, size_t n)
 {
@@ -607,14 +609,13 @@ static size_t csum_and_copy_to_pipe_iter(const void *addr, size_t bytes,
 
 size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 {
-       const char *from = addr;
        if (unlikely(iov_iter_is_pipe(i)))
                return copy_pipe_to_iter(addr, bytes, i);
        if (iter_is_iovec(i))
                might_fault();
-       iterate_and_advance(i, bytes, v,
-               copyout(v.iov_base, (from += v.iov_len) - v.iov_len, v.iov_len),
-               memcpy(v.iov_base, (from += v.iov_len) - v.iov_len, v.iov_len)
+       iterate_and_advance(i, bytes, v, off,
+               copyout(v.iov_base, addr + off, v.iov_len),
+               memcpy(v.iov_base, addr + off, v.iov_len)
        )
 
        return bytes;
@@ -703,17 +704,13 @@ static size_t copy_mc_pipe_to_iter(const void *addr, size_t bytes,
  */
 size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 {
-       const char *from = addr;
-
        if (unlikely(iov_iter_is_pipe(i)))
                return copy_mc_pipe_to_iter(addr, bytes, i);
        if (iter_is_iovec(i))
                might_fault();
-       __iterate_and_advance(i, bytes, v,
-               copyout_mc(v.iov_base, (from += v.iov_len) - v.iov_len,
-                          v.iov_len),
-               copy_mc_to_kernel(v.iov_base, (from += v.iov_len)
-                                       - v.iov_len, v.iov_len)
+       __iterate_and_advance(i, bytes, v, off,
+               copyout_mc(v.iov_base, addr + off, v.iov_len),
+               copy_mc_to_kernel(v.iov_base, addr + off, v.iov_len)
        )
 
        return bytes;
@@ -723,16 +720,15 @@ EXPORT_SYMBOL_GPL(_copy_mc_to_iter);
 
 size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
 {
-       char *to = addr;
        if (unlikely(iov_iter_is_pipe(i))) {
                WARN_ON(1);
                return 0;
        }
        if (iter_is_iovec(i))
                might_fault();
-       iterate_and_advance(i, bytes, v,
-               copyin((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len),
-               memcpy((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)
+       iterate_and_advance(i, bytes, v, off,
+               copyin(addr + off, v.iov_base, v.iov_len),
+               memcpy(addr + off, v.iov_base, v.iov_len)
        )
 
        return bytes;
@@ -741,15 +737,14 @@ EXPORT_SYMBOL(_copy_from_iter);
 
 size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)
 {
-       char *to = addr;
        if (unlikely(iov_iter_is_pipe(i))) {
                WARN_ON(1);
                return 0;
        }
-       iterate_and_advance(i, bytes, v,
-               __copy_from_user_inatomic_nocache((to += v.iov_len) - v.iov_len,
+       iterate_and_advance(i, bytes, v, off,
+               __copy_from_user_inatomic_nocache(addr + off,
                                         v.iov_base, v.iov_len),
-               memcpy((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)
+               memcpy(addr + off, v.iov_base, v.iov_len)
        )
 
        return bytes;
@@ -773,16 +768,13 @@ EXPORT_SYMBOL(_copy_from_iter_nocache);
  */
 size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)
 {
-       char *to = addr;
        if (unlikely(iov_iter_is_pipe(i))) {
                WARN_ON(1);
                return 0;
        }
-       iterate_and_advance(i, bytes, v,
-               __copy_from_user_flushcache((to += v.iov_len) - v.iov_len,
-                                        v.iov_base, v.iov_len),
-               memcpy_flushcache((to += v.iov_len) - v.iov_len, v.iov_base,
-                       v.iov_len)
+       iterate_and_advance(i, bytes, v, off,
+               __copy_from_user_flushcache(addr + off, v.iov_base, v.iov_len),
+               memcpy_flushcache(addr + off, v.iov_base, v.iov_len)
        )
 
        return bytes;
@@ -911,7 +903,7 @@ size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
 {
        if (unlikely(iov_iter_is_pipe(i)))
                return pipe_zero(bytes, i);
-       iterate_and_advance(i, bytes, v,
+       iterate_and_advance(i, bytes, v, count,
                clear_user(v.iov_base, v.iov_len),
                memset(v.iov_base, 0, v.iov_len)
        )
@@ -933,9 +925,9 @@ size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, size_t byt
                WARN_ON(1);
                return 0;
        }
-       iterate_and_advance(i, bytes, v,
-               copyin((p += v.iov_len) - v.iov_len, v.iov_base, v.iov_len),
-               memcpy((p += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)
+       iterate_and_advance(i, bytes, v, off,
+               copyin(p + off, v.iov_base, v.iov_len),
+               memcpy(p + off, v.iov_base, v.iov_len)
        )
        kunmap_atomic(kaddr);
        return bytes;
@@ -1656,28 +1648,22 @@ EXPORT_SYMBOL(iov_iter_get_pages_alloc);
 size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,
                               struct iov_iter *i)
 {
-       char *to = addr;
        __wsum sum, next;
-       size_t off = 0;
        sum = *csum;
        if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {
                WARN_ON(1);
                return 0;
        }
-       iterate_and_advance(i, bytes, v, ({
+       iterate_and_advance(i, bytes, v, off, ({
                next = csum_and_copy_from_user(v.iov_base,
-                                              (to += v.iov_len) - v.iov_len,
+                                              addr + off,
                                               v.iov_len);
-               if (next) {
+               if (next)
                        sum = csum_block_add(sum, next, off);
-                       off += v.iov_len;
-               }
                next ? 0 : v.iov_len;
        }), ({
-               sum = csum_and_memcpy((to += v.iov_len) - v.iov_len,
-                                     v.iov_base, v.iov_len,
+               sum = csum_and_memcpy(addr + off, v.iov_base, v.iov_len,
                                      sum, off);
-               off += v.iov_len;
        })
        )
        *csum = sum;
@@ -1689,33 +1675,27 @@ size_t csum_and_copy_to_iter(const void *addr, size_t bytes, void *_csstate,
                             struct iov_iter *i)
 {
        struct csum_state *csstate = _csstate;
-       const char *from = addr;
        __wsum sum, next;
-       size_t off;
 
        if (unlikely(iov_iter_is_pipe(i)))
                return csum_and_copy_to_pipe_iter(addr, bytes, _csstate, i);
 
        sum = csum_shift(csstate->csum, csstate->off);
-       off = 0;
        if (unlikely(iov_iter_is_discard(i))) {
                WARN_ON(1);     /* for now */
                return 0;
        }
-       iterate_and_advance(i, bytes, v, ({
-               next = csum_and_copy_to_user((from += v.iov_len) - v.iov_len,
+       iterate_and_advance(i, bytes, v, off, ({
+               next = csum_and_copy_to_user(addr + off,
                                             v.iov_base,
                                             v.iov_len);
-               if (next) {
+               if (next)
                        sum = csum_block_add(sum, next, off);
-                       off += v.iov_len;
-               }
                next ? 0 : v.iov_len;
        }), ({
                sum = csum_and_memcpy(v.iov_base,
-                                    (from += v.iov_len) - v.iov_len,
+                                    addr + off,
                                     v.iov_len, sum, off);
-               off += v.iov_len;
        })
        )
        csstate->csum = csum_shift(sum, csstate->off);