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SubjectRe: [Patch v2 14/15] CIFS: Add support for direct I/O write
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On 5/30/2018 3:48 PM, Long Li wrote:
> From: Long Li <longli@microsoft.com>
>
> Implement the function for direct I/O write. It doesn't support AIO, which
> will be implemented in a follow up patch.
>
> Signed-off-by: Long Li <longli@microsoft.com>
> ---
> fs/cifs/cifsfs.h | 1 +
> fs/cifs/file.c | 165 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 166 insertions(+)
>
> 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 e6e6f24..8c385b1 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -2461,6 +2461,35 @@ cifs_uncached_writedata_release(struct kref *refcount)
>
> static void collect_uncached_write_data(struct cifs_aio_ctx *ctx);
>
> +static void cifs_direct_writedata_release(struct kref *refcount)
> +{
> + int i;
> + struct cifs_writedata *wdata = container_of(refcount,
> + struct cifs_writedata, refcount);
> +
> + for (i = 0; i < wdata->nr_pages; i++)
> + put_page(wdata->pages[i]);
> +
> + cifs_writedata_release(refcount);
> +}
> +
> +static void cifs_direct_writev_complete(struct work_struct *work)
> +{
> + struct cifs_writedata *wdata = container_of(work,
> + struct cifs_writedata, work);
> + struct inode *inode = d_inode(wdata->cfile->dentry);
> + struct cifsInodeInfo *cifsi = CIFS_I(inode);
> +
> + spin_lock(&inode->i_lock);
> + cifs_update_eof(cifsi, wdata->offset, wdata->bytes);
> + if (cifsi->server_eof > inode->i_size)
> + i_size_write(inode, cifsi->server_eof);
> + spin_unlock(&inode->i_lock);
> +
> + complete(&wdata->done);
> + kref_put(&wdata->refcount, cifs_direct_writedata_release);
> +}
> +
> static void
> cifs_uncached_writev_complete(struct work_struct *work)
> {
> @@ -2703,6 +2732,142 @@ 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;
> + pid_t pid;
> + unsigned long nr_pages;
> + loff_t offset = iocb->ki_pos;
> + size_t len = iov_iter_count(from);
> + int rc;
> + struct cifs_writedata *wdata;
> +
> + /*
> + * 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;
> +
> + if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_RWPIDFORWARD)
> + pid = cfile->pid;
> + else
> + pid = current->tgid;
> +
> + do {
> + unsigned int wsize, credits;
> + struct page **pagevec;
> + size_t start;
> + ssize_t cur_len;
> +
> + rc = server->ops->wait_mtu_credits(server, cifs_sb->wsize,
> + &wsize, &credits);
> + if (rc)
> + break;
> +
> + 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;
> + }
> + if (cur_len < 0)
> + break;

This cur_len < 0 test is redundant with the prior if(), delete.
> +
> + nr_pages = (cur_len + start + PAGE_SIZE - 1) / PAGE_SIZE;

Am I misreading, or will this return be one more page than needed? If
start (the first byte offset) is > 0, nr_pages will already be one.
And if cur_len is 4KB, even if start is 0, nr_pages will be two.

> +
> + wdata = cifs_writedata_direct_alloc(pagevec,
> + cifs_direct_writev_complete);
> + if (!wdata) {
> + rc = -ENOMEM;
> + add_credits_and_wake_if(server, credits, 0);
> + break;
> + }
> +
> + wdata->nr_pages = nr_pages;
> + wdata->page_offset = start;
> + wdata->pagesz = PAGE_SIZE;
> + wdata->tailsz =
> + nr_pages > 1 ?
> + cur_len - (PAGE_SIZE - start) -
> + (nr_pages - 2) * PAGE_SIZE :
> + cur_len;
> +
> + wdata->sync_mode = WB_SYNC_ALL;
> + wdata->offset = (__u64)offset;
> + wdata->cfile = cifsFileInfo_get(cfile);
> + wdata->pid = pid;
> + wdata->bytes = cur_len;
> + wdata->credits = credits;
> +
> + rc = 0;
> + if (wdata->cfile->invalidHandle)
> + rc = cifs_reopen_file(wdata->cfile, false);
> +
> + if (!rc)
> + rc = server->ops->async_writev(wdata,
> + cifs_direct_writedata_release);
> +
> + if (rc) {
> + add_credits_and_wake_if(server, wdata->credits, 0);
> + kref_put(&wdata->refcount,
> + cifs_direct_writedata_release);
> + if (rc == -EAGAIN)
> + continue;
> + break;
> + }

Same comments as for previous patch re the if (rc) ladder, and
the break/continues both being better expressed as careful goto's.

> +
> + wait_for_completion(&wdata->done);
> + if (wdata->result) {
> + rc = wdata->result;
> + kref_put(&wdata->refcount,
> + cifs_direct_writedata_release);
> + if (rc == -EAGAIN)
> + continue;
> + break;
> + }
> +
> + kref_put(&wdata->refcount, cifs_direct_writedata_release);
> +
> + iov_iter_advance(from, cur_len);
> + total_written += cur_len;
> + offset += cur_len;
> + len -= cur_len;
> + } while (len);
> +
> + 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;
>

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