[RFC PATCH 28/53] netfs: Implement unbuffered/DIO write support

From: David Howells
Date: Fri Oct 13 2023 - 12:15:58 EST

Implement support for unbuffered writes and direct I/O writes. If the
write is misaligned with respect to the fscrypt block size, then RMW cycles
are performed if necessary. DIO writes are a special case of unbuffered
writes with extra restriction imposed, such as block size alignment
requirements.

Also provide a field that can tell the code to add some extra space onto
the bounce buffer for use by the filesystem in the case of a
content-encrypted file.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Jeff Layton <jlayton@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
cc: linux-mm@xxxxxxxxx
---
fs/afs/inode.c | 2 +-
fs/netfs/Makefile | 1 +
fs/netfs/direct_write.c | 159 +++++++++++++++++++++++++++++++++++
fs/netfs/internal.h | 6 ++
fs/netfs/io.c | 2 +-
fs/netfs/main.c | 12 +--
fs/netfs/objects.c | 6 +-
fs/netfs/output.c | 24 ++++++
include/linux/netfs.h | 4 +
include/trace/events/netfs.h | 4 +-
10 files changed, 210 insertions(+), 10 deletions(-)
create mode 100644 fs/netfs/direct_write.c

diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index 46bc5574d6f5..a8f4301aca9a 100644
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -250,7 +250,7 @@ static void afs_apply_status(struct afs_operation *op,
* what's on the server.
*/
vnode->netfs.remote_i_size = status->size;
- if (change_size) {
+ if (change_size || status->size > i_size_read(inode)) {
afs_set_i_size(vnode, status->size);
vnode->netfs.zero_point = status->size;
inode_set_ctime_to_ts(inode, t);
diff --git a/fs/netfs/Makefile b/fs/netfs/Makefile
index 27643557b443..d5c2809fc029 100644
--- a/fs/netfs/Makefile
+++ b/fs/netfs/Makefile
@@ -4,6 +4,7 @@ netfs-y := \
buffered_read.o \
buffered_write.o \
direct_read.o \
+ direct_write.o \
io.o \
iterator.o \
locking.o \
diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c
new file mode 100644
index 000000000000..b1a4921ac4a2
--- /dev/null
+++ b/fs/netfs/direct_write.c
@@ -0,0 +1,159 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Unbuffered and direct write support.
+ *
+ * Copyright (C) 2023 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@xxxxxxxxxx)
+ */
+
+#include <linux/export.h>
+#include <linux/uio.h>
+#include "internal.h"
+
+static void netfs_cleanup_dio_write(struct netfs_io_request *wreq)
+{
+ struct inode *inode = wreq->inode;
+ unsigned long long end = wreq->start + wreq->len;
+
+ if (!wreq->error &&
+ i_size_read(inode) < end) {
+ if (wreq->netfs_ops->update_i_size)
+ wreq->netfs_ops->update_i_size(inode, end);
+ else
+ i_size_write(inode, end);
+ }
+}
+
+/*
+ * Perform an unbuffered write where we may have to do an RMW operation on an
+ * encrypted file. This can also be used for direct I/O writes.
+ */
+ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,
+ struct netfs_group *netfs_group)
+{
+ struct netfs_io_request *wreq;
+ unsigned long long start = iocb->ki_pos;
+ unsigned long long end = start + iov_iter_count(iter);
+ ssize_t ret, n;
+ bool async = !is_sync_kiocb(iocb);
+
+ _enter("");
+
+ /* We're going to need a bounce buffer if what we transmit is going to
+ * be different in some way to the source buffer, e.g. because it gets
+ * encrypted/compressed or because it needs expanding to a block size.
+ */
+ // TODO
+
+ _debug("uw %llx-%llx", start, end);
+
+ wreq = netfs_alloc_request(iocb->ki_filp->f_mapping, iocb->ki_filp,
+ start, end - start,
+ iocb->ki_flags & IOCB_DIRECT ?
+ NETFS_DIO_WRITE : NETFS_UNBUFFERED_WRITE);
+ if (IS_ERR(wreq))
+ return PTR_ERR(wreq);
+
+ {
+ /* If this is an async op and we're not using a bounce buffer,
+ * we have to save the source buffer as the iterator is only
+ * good until we return. In such a case, extract an iterator
+ * to represent as much of the the output buffer as we can
+ * manage. Note that the extraction might not be able to
+ * allocate a sufficiently large bvec array and may shorten the
+ * request.
+ */
+ if (async || user_backed_iter(iter)) {
+ n = netfs_extract_user_iter(iter, wreq->len, &wreq->iter, 0);
+ if (n < 0) {
+ ret = n;
+ goto out;
+ }
+ wreq->direct_bv = (struct bio_vec *)wreq->iter.bvec;
+ wreq->direct_bv_count = n;
+ wreq->direct_bv_unpin = iov_iter_extract_will_pin(iter);
+ wreq->len = iov_iter_count(&wreq->iter);
+ } else {
+ wreq->iter = *iter;
+ }
+
+ wreq->io_iter = wreq->iter;
+ }
+
+ /* Copy the data into the bounce buffer and encrypt it. */
+ // TODO
+
+ /* Dispatch the write. */
+ __set_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags);
+ if (async)
+ wreq->iocb = iocb;
+ wreq->cleanup = netfs_cleanup_dio_write;
+ ret = netfs_begin_write(wreq, is_sync_kiocb(iocb),
+ iocb->ki_flags & IOCB_DIRECT ?
+ netfs_write_trace_dio_write :
+ netfs_write_trace_unbuffered_write);
+ if (ret < 0) {
+ _debug("begin = %zd", ret);
+ goto out;
+ }
+
+ if (!async) {
+ trace_netfs_rreq(wreq, netfs_rreq_trace_wait_ip);
+ wait_on_bit(&wreq->flags, NETFS_RREQ_IN_PROGRESS,
+ TASK_UNINTERRUPTIBLE);
+
+ ret = wreq->error;
+ _debug("waited = %zd", ret);
+ if (ret == 0) {
+ ret = wreq->transferred;
+ iocb->ki_pos += ret;
+ }
+ } else {
+ ret = -EIOCBQUEUED;
+ }
+
+out:
+ netfs_put_request(wreq, false, netfs_rreq_trace_put_return);
+ return ret;
+}
+
+/**
+ * netfs_unbuffered_write_iter - Unbuffered write to a file
+ * @iocb: IO state structure
+ * @from: iov_iter with data to write
+ *
+ * Do an unbuffered write to a file, writing the data directly to the server
+ * and not lodging the data in the pagecache.
+ *
+ * Return:
+ * * Negative error code if no data has been written at all of
+ * vfs_fsync_range() failed for a synchronous write
+ * * Number of bytes written, even for truncated writes
+ */
+ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+ struct file *file = iocb->ki_filp;
+ struct inode *inode = file->f_mapping->host;
+ ssize_t ret;
+
+ _enter("%llx,%zx,%llx", iocb->ki_pos, iov_iter_count(from), i_size_read(inode));
+
+ trace_netfs_write_iter(iocb, from);
+
+ ret = netfs_start_io_direct(inode);
+ if (ret < 0)
+ return ret;
+ ret = generic_write_checks(iocb, from);
+ if (ret < 0)
+ goto out;
+ ret = file_remove_privs(file);
+ if (ret < 0)
+ goto out;
+ ret = file_update_time(file);
+ if (ret < 0)
+ goto out;
+ ret = netfs_unbuffered_write_iter_locked(iocb, from, NULL);
+out:
+ netfs_end_io_direct(inode);
+ return ret;
+}
+EXPORT_SYMBOL(netfs_unbuffered_write_iter);
diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 0fe9aa5c6114..6a67abdf71c8 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -22,6 +22,12 @@ void netfs_rreq_unlock_folios(struct netfs_io_request *rreq);
int netfs_prefetch_for_write(struct file *file, struct folio *folio,
size_t offset, size_t len);

+/*
+ * direct_write.c
+ */
+ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *iter,
+ struct netfs_group *netfs_group);
+
/*
* io.c
*/
diff --git a/fs/netfs/io.c b/fs/netfs/io.c
index 921daecf5fde..36a3f720193a 100644
--- a/fs/netfs/io.c
+++ b/fs/netfs/io.c
@@ -643,7 +643,7 @@ static bool netfs_rreq_submit_slice(struct netfs_io_request *rreq,

subreq->debug_index = (*_debug_index)++;
subreq->start = rreq->start + rreq->submitted;
- subreq->len = rreq->len - rreq->submitted;
+ subreq->len = io_iter->count;

_debug("slice %llx,%zx,%zx", subreq->start, subreq->len, rreq->submitted);
list_add_tail(&subreq->rreq_link, &rreq->subrequests);
diff --git a/fs/netfs/main.c b/fs/netfs/main.c
index d0eb6654efa3..1cf10f9c4c1f 100644
--- a/fs/netfs/main.c
+++ b/fs/netfs/main.c
@@ -29,11 +29,13 @@ LIST_HEAD(netfs_io_requests);
DEFINE_SPINLOCK(netfs_proc_lock);

static const char *netfs_origins[nr__netfs_io_origin] = {
- [NETFS_READAHEAD] = "RA",
- [NETFS_READPAGE] = "RP",
- [NETFS_READ_FOR_WRITE] = "RW",
- [NETFS_WRITEBACK] = "WB",
- [NETFS_DIO_READ] = "DR",
+ [NETFS_READAHEAD] = "RA",
+ [NETFS_READPAGE] = "RP",
+ [NETFS_READ_FOR_WRITE] = "RW",
+ [NETFS_WRITEBACK] = "WB",
+ [NETFS_UNBUFFERED_WRITE] = "UW",
+ [NETFS_DIO_READ] = "DR",
+ [NETFS_DIO_WRITE] = "DW",
};

/*
diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index d46e957812a6..c1218b183197 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -20,8 +20,10 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
struct inode *inode = file ? file_inode(file) : mapping->host;
struct netfs_inode *ctx = netfs_inode(inode);
struct netfs_io_request *rreq;
- bool is_dio = (origin == NETFS_DIO_READ);
- bool cached = is_dio && netfs_is_cache_enabled(ctx);
+ bool is_unbuffered = (origin == NETFS_UNBUFFERED_WRITE ||
+ origin == NETFS_DIO_READ ||
+ origin == NETFS_DIO_WRITE);
+ bool cached = !is_unbuffered && netfs_is_cache_enabled(ctx);
int ret;

rreq = kzalloc(ctx->ops->io_request_size ?: sizeof(struct netfs_io_request),
diff --git a/fs/netfs/output.c b/fs/netfs/output.c
index e93453f4372d..bb42789c7a24 100644
--- a/fs/netfs/output.c
+++ b/fs/netfs/output.c
@@ -74,11 +74,21 @@ static void netfs_write_terminated(struct netfs_io_request *wreq, bool was_async
{
struct netfs_io_subrequest *subreq;
struct netfs_inode *ctx = netfs_inode(wreq->inode);
+ size_t transferred = 0;

_enter("R=%x[]", wreq->debug_id);

trace_netfs_rreq(wreq, netfs_rreq_trace_write_done);

+ list_for_each_entry(subreq, &wreq->subrequests, rreq_link) {
+ if (subreq->error || subreq->transferred == 0)
+ break;
+ transferred += subreq->transferred;
+ if (subreq->transferred < subreq->len)
+ break;
+ }
+ wreq->transferred = transferred;
+
list_for_each_entry(subreq, &wreq->subrequests, rreq_link) {
if (!subreq->error)
continue;
@@ -110,11 +120,25 @@ static void netfs_write_terminated(struct netfs_io_request *wreq, bool was_async

wreq->cleanup(wreq);

+ if (wreq->origin == NETFS_DIO_WRITE &&
+ wreq->mapping->nrpages) {
+ pgoff_t first = wreq->start >> PAGE_SHIFT;
+ pgoff_t last = (wreq->start + wreq->transferred - 1) >> PAGE_SHIFT;
+ invalidate_inode_pages2_range(wreq->mapping, first, last);
+ }
+
_debug("finished");
trace_netfs_rreq(wreq, netfs_rreq_trace_wake_ip);
clear_bit_unlock(NETFS_RREQ_IN_PROGRESS, &wreq->flags);
wake_up_bit(&wreq->flags, NETFS_RREQ_IN_PROGRESS);

+ if (wreq->iocb) {
+ wreq->iocb->ki_pos += transferred;
+ if (wreq->iocb->ki_complete)
+ wreq->iocb->ki_complete(
+ wreq->iocb, wreq->error ? wreq->error : transferred);
+ }
+
netfs_clear_subrequests(wreq, was_async);
netfs_put_request(wreq, was_async, netfs_rreq_trace_put_complete);
}
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 1d7e44d3c915..052d62625796 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -140,6 +140,7 @@ struct netfs_inode {
* on the server */
unsigned long flags;
#define NETFS_ICTX_ODIRECT 0 /* The file has DIO in progress */
+#define NETFS_ICTX_UNBUFFERED 1 /* I/O should not use the pagecache */
};

/*
@@ -228,7 +229,9 @@ enum netfs_io_origin {
NETFS_READPAGE, /* This read is a synchronous read */
NETFS_READ_FOR_WRITE, /* This read is to prepare a write */
NETFS_WRITEBACK, /* This write was triggered by writepages */
+ NETFS_UNBUFFERED_WRITE, /* This is an unbuffered write */
NETFS_DIO_READ, /* This is a direct I/O read */
+ NETFS_DIO_WRITE, /* This is a direct I/O write */
nr__netfs_io_origin
} __mode(byte);

@@ -385,6 +388,7 @@ ssize_t netfs_unbuffered_read_iter(struct kiocb *iocb, struct iov_iter *iter);
/* High-level write API */
ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
struct netfs_group *netfs_group);
+ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from);

/* Address operations API */
struct readahead_control;
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index cc7cb55f3420..60f98c99fe21 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -33,7 +33,9 @@
EM(NETFS_READPAGE, "RP") \
EM(NETFS_READ_FOR_WRITE, "RW") \
EM(NETFS_WRITEBACK, "WB") \
- E_(NETFS_DIO_READ, "DR")
+ EM(NETFS_UNBUFFERED_WRITE, "UW") \
+ EM(NETFS_DIO_READ, "DR") \
+ E_(NETFS_DIO_WRITE, "DW")

#define netfs_rreq_traces \
EM(netfs_rreq_trace_assess, "ASSESS ") \