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Subject[Patch v4 1/3] CIFS: Add support for direct I/O read
Date
From: Long Li <longli@microsoft.com>

With direct I/O read, we transfer the data directly from transport layer to
the user data buffer.

Change in v3: add support for kernel AIO

Change in v4:
Refactor common read code to __cifs_readv for direct and non-direct I/O.
Retry on direct I/O failure.

Signed-off-by: Long Li <longli@microsoft.com>
---
fs/cifs/cifsfs.h | 1 +
fs/cifs/cifsglob.h | 5 ++
fs/cifs/file.c | 219 +++++++++++++++++++++++++++++++++++++++++++----------
3 files changed, 186 insertions(+), 39 deletions(-)

diff --git a/fs/cifs/cifsfs.h b/fs/cifs/cifsfs.h
index 5f02318..7fba9aa 100644
--- a/fs/cifs/cifsfs.h
+++ b/fs/cifs/cifsfs.h
@@ -102,6 +102,7 @@ extern int cifs_open(struct inode *inode, struct file *file);
extern int cifs_close(struct inode *inode, struct file *file);
extern int cifs_closedir(struct inode *inode, struct file *file);
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_strict_writev(struct kiocb *iocb, struct iov_iter *from);
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 7f62c98..52248dd 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -1146,6 +1146,11 @@ struct cifs_aio_ctx {
unsigned int len;
unsigned int total_len;
bool should_dirty;
+ /*
+ * Indicates if this aio_ctx is for direct_io,
+ * If yes, iter is a copy of the user passed iov_iter
+ */
+ bool direct_io;
};

struct cifs_readdata;
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 87eece6..daab878 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2965,7 +2965,6 @@ cifs_uncached_readdata_release(struct kref *refcount)
kref_put(&rdata->ctx->refcount, cifs_aio_ctx_release);
for (i = 0; i < rdata->nr_pages; i++) {
put_page(rdata->pages[i]);
- rdata->pages[i] = NULL;
}
cifs_readdata_release(refcount);
}
@@ -3092,6 +3091,63 @@ cifs_uncached_copy_into_pages(struct TCP_Server_Info *server,
return uncached_fill_pages(server, rdata, iter, iter->count);
}

+static int cifs_resend_rdata(struct cifs_readdata *rdata,
+ struct list_head *rdata_list,
+ struct cifs_aio_ctx *ctx)
+{
+ int wait_retry = 0;
+ unsigned int rsize, credits;
+ int rc;
+ struct TCP_Server_Info *server = tlink_tcon(rdata->cfile->tlink)->ses->server;
+
+ /*
+ * Try to resend this rdata, waiting for credits up to 3 seconds.
+ * Note: we are attempting to resend the whole rdata not in segments
+ */
+ do {
+ rc = server->ops->wait_mtu_credits(server, rdata->bytes,
+ &rsize, &credits);
+
+ if (rc)
+ break;
+
+ if (rsize < rdata->bytes) {
+ add_credits_and_wake_if(server, credits, 0);
+ msleep(1000);
+ wait_retry++;
+ }
+ } while (rsize < rdata->bytes && wait_retry < 3);
+
+ /*
+ * If we can't find enough credits to send this rdata
+ * release the rdata and return failure, this will pass
+ * whatever I/O amount we have finished to VFS.
+ */
+ if (rsize < rdata->bytes) {
+ rc = -EBUSY;
+ goto out;
+ }
+
+ rc = -EAGAIN;
+ while (rc == -EAGAIN)
+ if (!rdata->cfile->invalidHandle ||
+ !(rc = cifs_reopen_file(rdata->cfile, true)))
+ rc = server->ops->async_readv(rdata);
+
+ if (!rc) {
+ /* Add to aio pending list */
+ list_add_tail(&rdata->list, rdata_list);
+ return 0;
+ }
+
+ add_credits_and_wake_if(server, rdata->credits, 0);
+out:
+ kref_put(&rdata->refcount,
+ cifs_uncached_readdata_release);
+
+ return rc;
+}
+
static int
cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
struct cifs_sb_info *cifs_sb, struct list_head *rdata_list,
@@ -3103,6 +3159,9 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
int rc;
pid_t pid;
struct TCP_Server_Info *server;
+ struct page **pagevec;
+ size_t start;
+ struct iov_iter direct_iov = ctx->iter;

server = tlink_tcon(open_file->tlink)->ses->server;

@@ -3111,6 +3170,9 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
else
pid = current->tgid;

+ if (ctx->direct_io)
+ iov_iter_advance(&direct_iov, offset - ctx->pos);
+
do {
rc = server->ops->wait_mtu_credits(server, cifs_sb->rsize,
&rsize, &credits);
@@ -3118,20 +3180,56 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
break;

cur_len = min_t(const size_t, len, rsize);
- npages = DIV_ROUND_UP(cur_len, PAGE_SIZE);

- /* allocate a readdata struct */
- rdata = cifs_readdata_alloc(npages,
+ if (ctx->direct_io) {
+
+ cur_len = iov_iter_get_pages_alloc(
+ &direct_iov, &pagevec,
+ cur_len, &start);
+ if (cur_len < 0) {
+ cifs_dbg(VFS,
+ "couldn't get user pages (cur_len=%zd)"
+ " iter type %d"
+ " iov_offset %zd count %zd\n",
+ cur_len, direct_iov.type, direct_iov.iov_offset,
+ direct_iov.count);
+ dump_stack();
+ break;
+ }
+ iov_iter_advance(&direct_iov, cur_len);
+
+ rdata = cifs_readdata_direct_alloc(
+ pagevec, cifs_uncached_readv_complete);
+ if (!rdata) {
+ add_credits_and_wake_if(server, credits, 0);
+ rc = -ENOMEM;
+ break;
+ }
+
+ npages = (cur_len + start + PAGE_SIZE-1) / PAGE_SIZE;
+ rdata->page_offset = start;
+ rdata->tailsz = npages > 1 ?
+ cur_len-(PAGE_SIZE-start)-(npages-2)*PAGE_SIZE :
+ cur_len;
+
+ } else {
+
+ npages = DIV_ROUND_UP(cur_len, PAGE_SIZE);
+ /* allocate a readdata struct */
+ rdata = cifs_readdata_alloc(npages,
cifs_uncached_readv_complete);
- if (!rdata) {
- add_credits_and_wake_if(server, credits, 0);
- rc = -ENOMEM;
- break;
- }
+ if (!rdata) {
+ add_credits_and_wake_if(server, credits, 0);
+ rc = -ENOMEM;
+ break;
+ }

- rc = cifs_read_allocate_pages(rdata, npages);
- if (rc)
- goto error;
+ rc = cifs_read_allocate_pages(rdata, npages);
+ if (rc)
+ goto error;
+
+ rdata->tailsz = PAGE_SIZE;
+ }

rdata->cfile = cifsFileInfo_get(open_file);
rdata->nr_pages = npages;
@@ -3139,7 +3237,6 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
rdata->bytes = cur_len;
rdata->pid = pid;
rdata->pagesz = PAGE_SIZE;
- rdata->tailsz = PAGE_SIZE;
rdata->read_into_pages = cifs_uncached_read_into_pages;
rdata->copy_into_pages = cifs_uncached_copy_into_pages;
rdata->credits = credits;
@@ -3153,9 +3250,11 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
if (rc) {
add_credits_and_wake_if(server, rdata->credits, 0);
kref_put(&rdata->refcount,
- cifs_uncached_readdata_release);
- if (rc == -EAGAIN)
+ cifs_uncached_readdata_release);
+ if (rc == -EAGAIN) {
+ iov_iter_revert(&direct_iov, cur_len);
continue;
+ }
break;
}

@@ -3211,45 +3310,62 @@ collect_uncached_read_data(struct cifs_aio_ctx *ctx)
* reading.
*/
if (got_bytes && got_bytes < rdata->bytes) {
- rc = cifs_readdata_to_iov(rdata, to);
+ rc = 0;
+ if (!ctx->direct_io)
+ rc = cifs_readdata_to_iov(rdata, to);
if (rc) {
kref_put(&rdata->refcount,
- cifs_uncached_readdata_release);
+ cifs_uncached_readdata_release);
continue;
}
}

- rc = cifs_send_async_read(
+ if (ctx->direct_io) {
+ /*
+ * Re-use rdata as this is a
+ * direct I/O
+ */
+ rc = cifs_resend_rdata(
+ rdata,
+ &tmp_list, ctx);
+ } else {
+ rc = cifs_send_async_read(
rdata->offset + got_bytes,
rdata->bytes - got_bytes,
rdata->cfile, cifs_sb,
&tmp_list, ctx);

+ kref_put(&rdata->refcount,
+ cifs_uncached_readdata_release);
+ }
+
list_splice(&tmp_list, &ctx->list);

- kref_put(&rdata->refcount,
- cifs_uncached_readdata_release);
goto again;
} else if (rdata->result)
rc = rdata->result;
- else
+ else if (!ctx->direct_io)
rc = cifs_readdata_to_iov(rdata, to);

/* if there was a short read -- discard anything left */
if (rdata->got_bytes && rdata->got_bytes < rdata->bytes)
rc = -ENODATA;
+
+ ctx->total_len += rdata->got_bytes;
}
list_del_init(&rdata->list);
kref_put(&rdata->refcount, cifs_uncached_readdata_release);
}

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

- ctx->total_len = ctx->len - iov_iter_count(to);
+ ctx->total_len = ctx->len - iov_iter_count(to);
+ }

cifs_stats_bytes_read(tcon, ctx->total_len);

@@ -3267,18 +3383,27 @@ collect_uncached_read_data(struct cifs_aio_ctx *ctx)
complete(&ctx->done);
}

-ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
+ssize_t __cifs_readv(struct kiocb *iocb, struct iov_iter *to, bool direct)
{
- struct file *file = iocb->ki_filp;
- ssize_t rc;
size_t len;
- ssize_t total_read = 0;
- loff_t offset = iocb->ki_pos;
+ struct file *file = iocb->ki_filp;
struct cifs_sb_info *cifs_sb;
- struct cifs_tcon *tcon;
struct cifsFileInfo *cfile;
+ struct cifs_tcon *tcon;
+ ssize_t rc, total_read = 0;
+ loff_t offset = iocb->ki_pos;
struct cifs_aio_ctx *ctx;

+ /*
+ * iov_iter_get_pages_alloc() doesn't work with ITER_KVEC,
+ * fall back to data copy read path
+ * this could be improved by getting pages directly in ITER_KVEC
+ */
+ if (direct && to->type & ITER_KVEC) {
+ cifs_dbg(FYI, "use non-direct cifs_user_readv for kvec I/O\n");
+ direct = false;
+ }
+
len = iov_iter_count(to);
if (!len)
return 0;
@@ -3305,14 +3430,20 @@ ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
if (to->type == ITER_IOVEC)
ctx->should_dirty = true;

- rc = setup_aio_ctx_iter(ctx, to, READ);
- if (rc) {
- kref_put(&ctx->refcount, cifs_aio_ctx_release);
- return rc;
+ if (direct) {
+ ctx->pos = offset;
+ ctx->direct_io = true;
+ ctx->iter = *to;
+ ctx->len = len;
+ } else {
+ rc = setup_aio_ctx_iter(ctx, to, READ);
+ if (rc) {
+ kref_put(&ctx->refcount, cifs_aio_ctx_release);
+ return rc;
+ }
+ len = ctx->len;
}

- len = ctx->len;
-
/* grab a lock here due to read response handlers can access ctx */
mutex_lock(&ctx->aio_mutex);

@@ -3354,6 +3485,16 @@ ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
return rc;
}

+ssize_t cifs_direct_readv(struct kiocb *iocb, struct iov_iter *to)
+{
+ return __cifs_readv(iocb, to, true);
+}
+
+ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
+{
+ return __cifs_readv(iocb, to, false);
+}
+
ssize_t
cifs_strict_readv(struct kiocb *iocb, struct iov_iter *to)
{
--
2.7.4
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