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netfs: Add support for DIO buffering

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Add a bvec array pointer and an iterator to netfs_io_request for either
holding a copy of a DIO iterator or a list of all the bits of buffer
pointed to by a DIO iterator.

There are two problems:  Firstly, if an iovec-class iov_iter is passed to
->read_iter() or ->write_iter(), this cannot be passed directly to
kernel_sendmsg() or kernel_recvmsg() as that may cause locking recursion if
a fault is generated, so we need to keep track of the pages involved
separately.

Secondly, if the I/O is asynchronous, we must copy the iov_iter describing
the buffer before returning to the caller as it may be immediately
deallocated.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
This commit is contained in:
David Howells 2021-07-09 08:41:17 +01:00
parent 92b6cc5d1e
commit 21d706d5cf
2 changed files with 13 additions and 0 deletions
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10
fs/netfs/objects.c
View File

@ -76,6 +76,7 @@ static void netfs_free_request(struct work_struct *work)
{
struct netfs_io_request *rreq =
container_of(work, struct netfs_io_request, work);
unsigned int i;
trace_netfs_rreq(rreq, netfs_rreq_trace_free);
netfs_proc_del_rreq(rreq);
@ -84,6 +85,15 @@ static void netfs_free_request(struct work_struct *work)
rreq->netfs_ops->free_request(rreq);
if (rreq->cache_resources.ops)
rreq->cache_resources.ops->end_operation(&rreq->cache_resources);
if (rreq->direct_bv) {
for (i = 0; i < rreq->direct_bv_count; i++) {
if (rreq->direct_bv[i].bv_page) {
if (rreq->direct_bv_unpin)
unpin_user_page(rreq->direct_bv[i].bv_page);
}
}
kvfree(rreq->direct_bv);
}
kfree_rcu(rreq, rcu);
netfs_stat_d(&netfs_n_rh_rreq);
}

3
include/linux/netfs.h
View File

@ -190,6 +190,8 @@ struct netfs_io_request {
struct iov_iter iter; /* Unencrypted-side iterator */
struct iov_iter io_iter; /* I/O (Encrypted-side) iterator */
void *netfs_priv; /* Private data for the netfs */
struct bio_vec *direct_bv; /* DIO buffer list (when handling iovec-iter) */
unsigned int direct_bv_count; /* Number of elements in direct_bv[] */
unsigned int debug_id;
atomic_t nr_outstanding; /* Number of ops in progress */
atomic_t nr_copy_ops; /* Number of copy-to-cache ops in progress */
@ -197,6 +199,7 @@ struct netfs_io_request {
size_t len; /* Length of the request */
short error; /* 0 or error that occurred */
enum netfs_io_origin origin; /* Origin of the request */
bool direct_bv_unpin; /* T if direct_bv[] must be unpinned */
loff_t i_size; /* Size of the file */
loff_t start; /* Start position */
pgoff_t no_unlock_folio; /* Don't unlock this folio after read */