summaryrefslogtreecommitdiff
path: root/include
diff options
context:
space:
mode:
authorJens Axboe <axboe@kernel.dk>2021-09-10 11:18:36 -0600
committerJens Axboe <axboe@kernel.dk>2021-09-14 08:12:18 -0600
commit8fb0f47a9d7acf620d0fd97831b69da9bc5e22ed (patch)
tree89e9ff5375b25a40b66986e284fdf7a7592ed3b1 /include
parentd6c338a741295c04ed84679153448b2fffd2c9cf (diff)
iov_iter: add helper to save iov_iter state
In an ideal world, when someone is passed an iov_iter and returns X bytes, then X bytes would have been consumed/advanced from the iov_iter. But we have use cases that always consume the entire iterator, a few examples of that are iomap and bdev O_DIRECT. This means we cannot rely on the state of the iov_iter once we've called ->read_iter() or ->write_iter(). This would be easier if we didn't always have to deal with truncate of the iov_iter, as rewinding would be trivial without that. We recently added a commit to track the truncate state, but that grew the iov_iter by 8 bytes and wasn't the best solution. Implement a helper to save enough of the iov_iter state to sanely restore it after we've called the read/write iterator helpers. This currently only works for IOVEC/BVEC/KVEC as that's all we need, support for other iterator types are left as an exercise for the reader. Link: https://lore.kernel.org/linux-fsdevel/CAHk-=wiacKV4Gh-MYjteU0LwNBSGpWrK-Ov25HdqB1ewinrFPg@mail.gmail.com/ Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include')
-rw-r--r--include/linux/uio.h15
1 files changed, 15 insertions, 0 deletions
diff --git a/include/linux/uio.h b/include/linux/uio.h
index 5265024e8b90..984c4ab74859 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -27,6 +27,12 @@ enum iter_type {
ITER_DISCARD,
};
+struct iov_iter_state {
+ size_t iov_offset;
+ size_t count;
+ unsigned long nr_segs;
+};
+
struct iov_iter {
u8 iter_type;
bool data_source;
@@ -55,6 +61,14 @@ static inline enum iter_type iov_iter_type(const struct iov_iter *i)
return i->iter_type;
}
+static inline void iov_iter_save_state(struct iov_iter *iter,
+ struct iov_iter_state *state)
+{
+ state->iov_offset = iter->iov_offset;
+ state->count = iter->count;
+ state->nr_segs = iter->nr_segs;
+}
+
static inline bool iter_is_iovec(const struct iov_iter *i)
{
return iov_iter_type(i) == ITER_IOVEC;
@@ -233,6 +247,7 @@ ssize_t iov_iter_get_pages(struct iov_iter *i, struct page **pages,
ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, struct page ***pages,
size_t maxsize, size_t *start);
int iov_iter_npages(const struct iov_iter *i, int maxpages);
+void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state);
const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags);