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SubjectRE: [Patch v2 14/15] CIFS: Add support for direct I/O write
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> 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@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.

I think the calculation is correct, assuming cur_len > 0. (which should be the case if we reach here)

If cur_len is 4kb and start is 0, nr_pages will be 1.

>
> > +
> > + 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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