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iov_iter: overlay struct iovec and ubuf/len 

Add an internal struct iovec that we can return as a pointer, with the
fields of the iovec overlapping with the ITER_UBUF ubuf and length
fields.

Then we can have iter_iov() check for the appropriate type, and return
&iter->__ubuf_iovec for ITER_UBUF and iter->__iov for ITER_IOVEC and
things will magically work out for a single segment request regardless
of either type.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2023-03-28 14:21:06 -06:00
parent cd0bd57a9d
commit 747b1f65d3
1 changed files with 35 additions and 9 deletions
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44
include/linux/uio.h
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@ -49,15 +49,35 @@ struct iov_iter {
size_t iov_offset;
int last_offset;
};
size_t count;
/*
* Hack alert: overlay ubuf_iovec with iovec + count, so
* that the members resolve correctly regardless of the type
* of iterator used. This means that you can use:
*
* &iter->__ubuf_iovec or iter->__iov
*
* interchangably for the user_backed cases, hence simplifying
* some of the cases that need to deal with both.
*/
union {
/* use iter_iov() to get the current vec */
const struct iovec *__iov;
const struct kvec *kvec;
const struct bio_vec *bvec;
struct xarray *xarray;
struct pipe_inode_info *pipe;
void __user *ubuf;
/*
* This really should be a const, but we cannot do that without
* also modifying any of the zero-filling iter init functions.
* Leave it non-const for now, but it should be treated as such.
*/
struct iovec __ubuf_iovec;
struct {
union {
/* use iter_iov() to get the current vec */
const struct iovec *__iov;
const struct kvec *kvec;
const struct bio_vec *bvec;
struct xarray *xarray;
struct pipe_inode_info *pipe;
void __user *ubuf;
};
size_t count;
};
};
union {
unsigned long nr_segs;
@ -69,7 +89,13 @@ struct iov_iter {
};
};
#define iter_iov(iter) (iter)->__iov
static inline const struct iovec *iter_iov(const struct iov_iter *iter)
{
if (iter->iter_type == ITER_UBUF)
return (const struct iovec *) &iter->__ubuf_iovec;
return iter->__iov;
}
#define iter_iov_addr(iter) (iter_iov(iter)->iov_base + (iter)->iov_offset)
#define iter_iov_len(iter) (iter_iov(iter)->iov_len - (iter)->iov_offset)