RE: [Patch v2 14/15] CIFS: Add support for direct I/O write

[Long Li]

> Subject: Re: [Patch v2 14/15] CIFS: Add support for direct I/O write
> 
> On 6/26/2018 12:39 AM, Long Li wrote:
> >> Subject: Re: [Patch v2 14/15] CIFS: Add support for direct I/O write
> >>
> >> On 5/30/2018 3:48 PM, Long Li wrote:
> >>> From: Long Li <longli@xxxxxxxxxxxxx>
> >>>
> >>> 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@xxxxxxxxxxxxx>
> >>> ---
> >>>    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.
> >
> > I think the calculation is correct, assuming cur_len > 0. (which
> > should be the case if we reach here)
> 
> Err, cur_len could possibly be zero, the prior line only breaks the loop if
> cur_len < 0.

I will look into this. It's a good idea to return error on 0 since we have no way to proceed.

> 
> > If cur_len is 4kb and start is 0, nr_pages will be 1.
> 
> Hmm, I guess. But again, it seems as if this page handling is all being coded
> inline, in subtly different ways. I'm just concerned about clarity and
> robustness. To me, if it's hard to review, it's even harder to maintain.

I will address this in an updated patch.

> 
> Tom.
> 
> >
> >>
> >>> +
> >>> +		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;
> >>>