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iov_iter: separate direction from flavour

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Instead of having them mixed in iter->type, use separate ->iter_type
and ->data_source (u8 and bool resp.)  And don't bother with (pseudo-)
bitmap for the former - microoptimizations from being able to check
if the flavour is one of two values are not worth the confusion for
optimizer.  It can't prove that we never get e.g. ITER_IOVEC | ITER_PIPE,
so we end up with extra headache.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2021-04-22 14:50:39 -04:00
parent 556351c1c0
commit 8cd54c1c84
2 changed files with 58 additions and 51 deletions
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24
include/linux/uio.h
View File

@ -19,21 +19,17 @@ struct kvec {
enum iter_type {
/* iter types */
ITER_IOVEC = 4,
ITER_KVEC = 8,
ITER_BVEC = 16,
ITER_PIPE = 32,
ITER_DISCARD = 64,
ITER_XARRAY = 128,
ITER_IOVEC,
ITER_KVEC,
ITER_BVEC,
ITER_PIPE,
ITER_XARRAY,
ITER_DISCARD,
};
struct iov_iter {
/*
* Bit 0 is the read/write bit, set if we're writing.
* Bit 1 is the BVEC_FLAG_NO_REF bit, set if type is a bvec and
* the caller isn't expecting to drop a page reference when done.
*/
unsigned int type;
u8 iter_type;
bool data_source;
size_t iov_offset;
size_t count;
union {
@ -55,7 +51,7 @@ struct iov_iter {
static inline enum iter_type iov_iter_type(const struct iov_iter *i)
{
return i->type & ~(READ | WRITE);
return i->iter_type;
}
static inline bool iter_is_iovec(const struct iov_iter *i)
@ -90,7 +86,7 @@ static inline bool iov_iter_is_xarray(const struct iov_iter *i)
static inline unsigned char iov_iter_rw(const struct iov_iter *i)
{
return i->type & (READ | WRITE);
return i->data_source ? WRITE : READ;
}
/*

85
lib/iov_iter.c
View File

@ -489,19 +489,15 @@ void iov_iter_init(struct iov_iter *i, unsigned int direction,
size_t count)
{
WARN_ON(direction & ~(READ | WRITE));
direction &= READ | WRITE;
/* It will get better. Eventually... */
if (uaccess_kernel()) {
i->type = ITER_KVEC | direction;
i->kvec = (struct kvec *)iov;
} else {
i->type = ITER_IOVEC | direction;
i->iov = iov;
}
i->nr_segs = nr_segs;
i->iov_offset = 0;
i->count = count;
WARN_ON_ONCE(uaccess_kernel());
*i = (struct iov_iter) {
.iter_type = ITER_IOVEC,
.data_source = direction,
.iov = iov,
.nr_segs = nr_segs,
.iov_offset = 0,
.count = count
};
}
EXPORT_SYMBOL(iov_iter_init);
@ -1218,11 +1214,14 @@ void iov_iter_kvec(struct iov_iter *i, unsigned int direction,
size_t count)
{
WARN_ON(direction & ~(READ | WRITE));
i->type = ITER_KVEC | (direction & (READ | WRITE));
i->kvec = kvec;
i->nr_segs = nr_segs;
i->iov_offset = 0;
i->count = count;
*i = (struct iov_iter){
.iter_type = ITER_KVEC,
.data_source = direction,
.kvec = kvec,
.nr_segs = nr_segs,
.iov_offset = 0,
.count = count
};
}
EXPORT_SYMBOL(iov_iter_kvec);
@ -1231,11 +1230,14 @@ void iov_iter_bvec(struct iov_iter *i, unsigned int direction,
size_t count)
{
WARN_ON(direction & ~(READ | WRITE));
i->type = ITER_BVEC | (direction & (READ | WRITE));
i->bvec = bvec;
i->nr_segs = nr_segs;
i->iov_offset = 0;
i->count = count;
*i = (struct iov_iter){
.iter_type = ITER_BVEC,
.data_source = direction,
.bvec = bvec,
.nr_segs = nr_segs,
.iov_offset = 0,
.count = count
};
}
EXPORT_SYMBOL(iov_iter_bvec);
@ -1245,12 +1247,15 @@ void iov_iter_pipe(struct iov_iter *i, unsigned int direction,
{
BUG_ON(direction != READ);
WARN_ON(pipe_full(pipe->head, pipe->tail, pipe->ring_size));
i->type = ITER_PIPE | READ;
i->pipe = pipe;
i->head = pipe->head;
i->iov_offset = 0;
i->count = count;
i->start_head = i->head;
*i = (struct iov_iter){
.iter_type = ITER_PIPE,
.data_source = false,
.pipe = pipe,
.head = pipe->head,
.start_head = pipe->head,
.iov_offset = 0,
.count = count
};
}
EXPORT_SYMBOL(iov_iter_pipe);
@ -1271,11 +1276,14 @@ void iov_iter_xarray(struct iov_iter *i, unsigned int direction,
struct xarray *xarray, loff_t start, size_t count)
{
BUG_ON(direction & ~1);
i->type = ITER_XARRAY | (direction & (READ | WRITE));
i->xarray = xarray;
i->xarray_start = start;
i->count = count;
i->iov_offset = 0;
*i = (struct iov_iter) {
.iter_type = ITER_XARRAY,
.data_source = direction,
.xarray = xarray,
.xarray_start = start,
.count = count,
.iov_offset = 0
};
}
EXPORT_SYMBOL(iov_iter_xarray);
@ -1291,9 +1299,12 @@ EXPORT_SYMBOL(iov_iter_xarray);
void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count)
{
BUG_ON(direction != READ);
i->type = ITER_DISCARD | READ;
i->count = count;
i->iov_offset = 0;
*i = (struct iov_iter){
.iter_type = ITER_DISCARD,
.data_source = false,
.count = count,
.iov_offset = 0
};
}
EXPORT_SYMBOL(iov_iter_discard);