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    Subject[PATCH V3 (resend) 4/7] 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: add support for kernel AIO

    Signed-off-by: Long Li <longli@microsoft.com>
    ---
    fs/cifs/cifsfs.h | 1 +
    fs/cifs/file.c | 196 ++++++++++++++++++++++++++++++++++++++++++++++---------
    2 files changed, 166 insertions(+), 31 deletions(-)

    diff --git a/fs/cifs/cifsfs.h b/fs/cifs/cifsfs.h
    index ed5479c..cc54051 100644
    --- a/fs/cifs/cifsfs.h
    +++ b/fs/cifs/cifsfs.h
    @@ -104,6 +104,7 @@ 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 6a939fa..2a5d209 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 %zd count"
    + " %zd\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 +2741,102 @@ 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.
    + * this could be improved by getting pages directly in ITER_KVEC
    + */
    + 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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