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Subject[Patch v3 15/16] CIFS: Add support for direct I/O write
Date
From: Long Li <longli@microsoft.com>

With direct I/O write, user supplied buffers are pinned to the memory and data
are transferred directly from user buffers to the transport layer.

Change in v3: added support for kernel AIO

Signed-off-by: Long Li <longli@microsoft.com>
---
fs/cifs/cifsfs.h | 1 +
fs/cifs/file.c | 195 ++++++++++++++++++++++++++++++++++++++++++++++---------
2 files changed, 165 insertions(+), 31 deletions(-)

diff --git a/fs/cifs/cifsfs.h b/fs/cifs/cifsfs.h
index 7fba9aa..e9c5103 100644
--- a/fs/cifs/cifsfs.h
+++ b/fs/cifs/cifsfs.h
@@ -105,6 +105,7 @@ extern ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to);
extern ssize_t cifs_direct_readv(struct kiocb *iocb, struct iov_iter *to);
extern ssize_t cifs_strict_readv(struct kiocb *iocb, struct iov_iter *to);
extern ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from);
+extern ssize_t cifs_direct_writev(struct kiocb *iocb, struct iov_iter *from);
extern ssize_t cifs_strict_writev(struct kiocb *iocb, struct iov_iter *from);
extern int cifs_lock(struct file *, int, struct file_lock *);
extern int cifs_fsync(struct file *, loff_t, loff_t, int);
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 476b2a1..76e0266 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2537,6 +2537,8 @@ cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from,
loff_t saved_offset = offset;
pid_t pid;
struct TCP_Server_Info *server;
+ struct page **pagevec;
+ size_t start;

if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_RWPIDFORWARD)
pid = open_file->pid;
@@ -2553,38 +2555,74 @@ cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from,
if (rc)
break;

- nr_pages = get_numpages(wsize, len, &cur_len);
- wdata = cifs_writedata_alloc(nr_pages,
+ if (ctx->direct_io) {
+ cur_len = iov_iter_get_pages_alloc(
+ from, &pagevec, wsize, &start);
+ if (cur_len < 0) {
+ cifs_dbg(VFS,
+ "direct_writev couldn't get user pages "
+ "(rc=%zd) iter type %d iov_offset %lu count"
+ " %lu\n",
+ cur_len, from->type,
+ from->iov_offset, from->count);
+ dump_stack();
+ break;
+ }
+ iov_iter_advance(from, cur_len);
+
+ nr_pages = (cur_len + start + PAGE_SIZE - 1) / PAGE_SIZE;
+
+ wdata = cifs_writedata_direct_alloc(pagevec,
cifs_uncached_writev_complete);
- if (!wdata) {
- rc = -ENOMEM;
- add_credits_and_wake_if(server, credits, 0);
- break;
- }
+ if (!wdata) {
+ rc = -ENOMEM;
+ add_credits_and_wake_if(server, credits, 0);
+ break;
+ }

- rc = cifs_write_allocate_pages(wdata->pages, nr_pages);
- if (rc) {
- kfree(wdata);
- add_credits_and_wake_if(server, credits, 0);
- break;
- }

- num_pages = nr_pages;
- rc = wdata_fill_from_iovec(wdata, from, &cur_len, &num_pages);
- if (rc) {
- for (i = 0; i < nr_pages; i++)
- put_page(wdata->pages[i]);
- kfree(wdata);
- add_credits_and_wake_if(server, credits, 0);
- break;
- }
+ wdata->page_offset = start;
+ wdata->tailsz =
+ nr_pages > 1 ?
+ cur_len - (PAGE_SIZE - start) -
+ (nr_pages - 2) * PAGE_SIZE :
+ cur_len;
+ } else {
+ nr_pages = get_numpages(wsize, len, &cur_len);
+ wdata = cifs_writedata_alloc(nr_pages,
+ cifs_uncached_writev_complete);
+ if (!wdata) {
+ rc = -ENOMEM;
+ add_credits_and_wake_if(server, credits, 0);
+ break;
+ }

- /*
- * Bring nr_pages down to the number of pages we actually used,
- * and free any pages that we didn't use.
- */
- for ( ; nr_pages > num_pages; nr_pages--)
- put_page(wdata->pages[nr_pages - 1]);
+ rc = cifs_write_allocate_pages(wdata->pages, nr_pages);
+ if (rc) {
+ kfree(wdata);
+ add_credits_and_wake_if(server, credits, 0);
+ break;
+ }
+
+ num_pages = nr_pages;
+ rc = wdata_fill_from_iovec(wdata, from, &cur_len, &num_pages);
+ if (rc) {
+ for (i = 0; i < nr_pages; i++)
+ put_page(wdata->pages[i]);
+ kfree(wdata);
+ add_credits_and_wake_if(server, credits, 0);
+ break;
+ }
+
+ /*
+ * Bring nr_pages down to the number of pages we actually used,
+ * and free any pages that we didn't use.
+ */
+ for ( ; nr_pages > num_pages; nr_pages--)
+ put_page(wdata->pages[nr_pages - 1]);
+
+ wdata->tailsz = cur_len - ((nr_pages - 1) * PAGE_SIZE);
+ }

wdata->sync_mode = WB_SYNC_ALL;
wdata->nr_pages = nr_pages;
@@ -2593,7 +2631,6 @@ cifs_write_from_iter(loff_t offset, size_t len, struct iov_iter *from,
wdata->pid = pid;
wdata->bytes = cur_len;
wdata->pagesz = PAGE_SIZE;
- wdata->tailsz = cur_len - ((nr_pages - 1) * PAGE_SIZE);
wdata->credits = credits;
wdata->ctx = ctx;
kref_get(&ctx->refcount);
@@ -2687,8 +2724,9 @@ static void collect_uncached_write_data(struct cifs_aio_ctx *ctx)
kref_put(&wdata->refcount, cifs_uncached_writedata_release);
}

- for (i = 0; i < ctx->npages; i++)
- put_page(ctx->bv[i].bv_page);
+ if (!ctx->direct_io)
+ for (i = 0; i < ctx->npages; i++)
+ put_page(ctx->bv[i].bv_page);

cifs_stats_bytes_written(tcon, ctx->total_len);
set_bit(CIFS_INO_INVALID_MAPPING, &CIFS_I(dentry->d_inode)->flags);
@@ -2703,6 +2741,101 @@ static void collect_uncached_write_data(struct cifs_aio_ctx *ctx)
complete(&ctx->done);
}

+ssize_t cifs_direct_writev(struct kiocb *iocb, struct iov_iter *from)
+{
+ struct file *file = iocb->ki_filp;
+ ssize_t total_written = 0;
+ struct cifsFileInfo *cfile;
+ struct cifs_tcon *tcon;
+ struct cifs_sb_info *cifs_sb;
+ struct TCP_Server_Info *server;
+ size_t len = iov_iter_count(from);
+ int rc;
+ struct cifs_aio_ctx *ctx;
+
+ /*
+ * iov_iter_get_pages_alloc doesn't work with ITER_KVEC.
+ * In this case, fall back to non-direct write function.
+ */
+ if (from->type & ITER_KVEC) {
+ cifs_dbg(FYI, "use non-direct cifs_user_writev for kvec I/O\n");
+ return cifs_user_writev(iocb, from);
+ }
+
+ rc = generic_write_checks(iocb, from);
+ if (rc <= 0)
+ return rc;
+
+ cifs_sb = CIFS_FILE_SB(file);
+ cfile = file->private_data;
+ tcon = tlink_tcon(cfile->tlink);
+ server = tcon->ses->server;
+
+ if (!server->ops->async_writev)
+ return -ENOSYS;
+
+ ctx = cifs_aio_ctx_alloc();
+ if (!ctx)
+ return -ENOMEM;
+
+ ctx->cfile = cifsFileInfo_get(cfile);
+
+ if (!is_sync_kiocb(iocb))
+ ctx->iocb = iocb;
+
+ ctx->pos = iocb->ki_pos;
+
+ ctx->direct_io = true;
+ ctx->iter = *from;
+ ctx->len = len;
+
+ /* grab a lock here due to read response handlers can access ctx */
+ mutex_lock(&ctx->aio_mutex);
+
+ rc = cifs_write_from_iter(iocb->ki_pos, ctx->len, from,
+ cfile, cifs_sb, &ctx->list, ctx);
+
+ /*
+ * If at least one write was successfully sent, then discard any rc
+ * value from the later writes. If the other write succeeds, then
+ * we'll end up returning whatever was written. If it fails, then
+ * we'll get a new rc value from that.
+ */
+ if (!list_empty(&ctx->list))
+ rc = 0;
+
+ mutex_unlock(&ctx->aio_mutex);
+
+ if (rc) {
+ kref_put(&ctx->refcount, cifs_aio_ctx_release);
+ return rc;
+ }
+
+ if (!is_sync_kiocb(iocb)) {
+ kref_put(&ctx->refcount, cifs_aio_ctx_release);
+ return -EIOCBQUEUED;
+ }
+
+ rc = wait_for_completion_killable(&ctx->done);
+ if (rc) {
+ mutex_lock(&ctx->aio_mutex);
+ ctx->rc = rc = -EINTR;
+ total_written = ctx->total_len;
+ mutex_unlock(&ctx->aio_mutex);
+ } else {
+ rc = ctx->rc;
+ total_written = ctx->total_len;
+ }
+
+ kref_put(&ctx->refcount, cifs_aio_ctx_release);
+
+ if (unlikely(!total_written))
+ return rc;
+
+ iocb->ki_pos += total_written;
+ return total_written;
+}
+
ssize_t cifs_user_writev(struct kiocb *iocb, struct iov_iter *from)
{
struct file *file = iocb->ki_filp;
--
2.7.4
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