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SubjectRe: [Patch v2 13/15] CIFS: Add support for direct I/O read
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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 read. 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 | 149 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 150 insertions(+)
>
> 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/file.c b/fs/cifs/file.c
> index 87eece6..e6e6f24 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -2955,6 +2955,18 @@ cifs_read_allocate_pages(struct cifs_readdata *rdata, unsigned int nr_pages)
> return rc;
> }
>
> +static void cifs_direct_readdata_release(struct kref *refcount)
> +{
> + struct cifs_readdata *rdata = container_of(refcount,
> + struct cifs_readdata, refcount);
> + unsigned int i;
> +
> + for (i = 0; i < rdata->nr_pages; i++)
> + put_page(rdata->pages[i]);
> +
> + cifs_readdata_release(refcount);
> +}
> +
> static void
> cifs_uncached_readdata_release(struct kref *refcount)
> {
> @@ -3267,6 +3279,143 @@ collect_uncached_read_data(struct cifs_aio_ctx *ctx)
> complete(&ctx->done);
> }
>
> +static void cifs_direct_readv_complete(struct work_struct *work)
> +{
> + struct cifs_readdata *rdata =
> + container_of(work, struct cifs_readdata, work);
> +
> + complete(&rdata->done);
> + kref_put(&rdata->refcount, cifs_direct_readdata_release);
> +}
> +
> +ssize_t cifs_direct_readv(struct kiocb *iocb, struct iov_iter *to)
> +{
> + size_t len, cur_len, start;
> + unsigned int npages, rsize, credits;
> + struct file *file;
> + struct cifs_sb_info *cifs_sb;
> + struct cifsFileInfo *cfile;
> + struct cifs_tcon *tcon;
> + struct page **pagevec;
> + ssize_t rc, total_read = 0;
> + struct TCP_Server_Info *server;
> + loff_t offset = iocb->ki_pos;
> + pid_t pid;
> + struct cifs_readdata *rdata;
> +
> + /*
> + * iov_iter_get_pages_alloc() doesn't work with ITER_KVEC,
> + * fall back to data copy read path
> + */
> + if (to->type & ITER_KVEC) {
> + cifs_dbg(FYI, "use non-direct cifs_user_readv for kvec I/O\n");
> + return cifs_user_readv(iocb, to);
> + }
> +
> + len = iov_iter_count(to);
> + if (!len)
> + return 0;
> +
> + file = iocb->ki_filp;
> + cifs_sb = CIFS_FILE_SB(file);
> + cfile = file->private_data;
> + tcon = tlink_tcon(cfile->tlink);
> + server = tcon->ses->server;
> +
> + if (!server->ops->async_readv)
> + return -ENOSYS;
> +
> + if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_RWPIDFORWARD)
> + pid = cfile->pid;
> + else
> + pid = current->tgid;
> +
> + if ((file->f_flags & O_ACCMODE) == O_WRONLY)
> + cifs_dbg(FYI, "attempting read on write only file instance\n");

Confusing. Maybe "attempting read on write-only filehandle"?

> +
> + do {
> + rc = server->ops->wait_mtu_credits(server, cifs_sb->rsize,
> + &rsize, &credits);
> + if (rc)
> + break;
> +
> + cur_len = min_t(const size_t, len, rsize);
> +
> + rc = iov_iter_get_pages_alloc(to, &pagevec, cur_len, &start);
> + if (rc < 0) {
> + cifs_dbg(VFS,
> + "couldn't get user pages (rc=%zd) iter type %d"
> + " iov_offset %lu count %lu\n",
> + rc, to->type, to->iov_offset, to->count);
> + dump_stack();
> + break;
> + }
> +
> + rdata = cifs_readdata_direct_alloc(
> + pagevec, cifs_direct_readv_complete);
> + if (!rdata) {
> + add_credits_and_wake_if(server, credits, 0);
> + rc = -ENOMEM;
> + break;
> + }
> +
> + npages = (rc + start + PAGE_SIZE-1) / PAGE_SIZE;
> + rdata->nr_pages = npages;
> + rdata->page_offset = start;
> + rdata->pagesz = PAGE_SIZE;
> + rdata->tailsz = npages > 1 ?
> + rc-(PAGE_SIZE-start)-(npages-2)*PAGE_SIZE :
> + rc;

This expression makes my head hurt. Surely it can be simplified, or
expressed in a clearer way.

> + cur_len = rc;
> +
> + rdata->cfile = cifsFileInfo_get(cfile);
> + rdata->offset = offset;
> + rdata->bytes = rc;
> + rdata->pid = pid;
> + rdata->read_into_pages = cifs_uncached_read_into_pages;
> + rdata->copy_into_pages = cifs_uncached_copy_into_pages;
> + rdata->credits = credits;
> +
> + rc = 0;
> + if (rdata->cfile->invalidHandle)
> + rc = cifs_reopen_file(rdata->cfile, true);
> +
> + if (!rc)
> + rc = server->ops->async_readv(rdata);
> +
> + if (rc) {

This whole rc thing is messy. Initializing to zero, setting only in
one case, then testing the result, then setting it again, is twisted.
I actually think a goto or two would read much more clearly.

> + add_credits_and_wake_if(server, rdata->credits, 0);
> + kref_put(&rdata->refcount,
> + cifs_direct_readdata_release);
> + if (rc == -EAGAIN)
> + continue;
> + break;

It's worth a comment here that this either breaks or continues the
entire do {} while (); and btw when it breaks it does *not* return "rc".
Again, maybe a goto instead of a break?

> + }
> +
> + wait_for_completion(&rdata->done);
> + rc = rdata->result;
> + if (rc) {
> + kref_put(
> + &rdata->refcount,
> + cifs_direct_readdata_release);
> + if (rc == -EAGAIN)
> + continue;
> + break;

Ditto.

> + }
> +
> + total_read += rdata->got_bytes;
> + kref_put(&rdata->refcount, cifs_direct_readdata_release);
> +
> + iov_iter_advance(to, cur_len);
> + len -= cur_len;
> + offset += cur_len;
> + } while (len);
> +
> + iocb->ki_pos += total_read;
> +
> + return total_read;
> +}
> +
> ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
> {
> struct file *file = iocb->ki_filp;
>

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