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    Subject[Patch v2 13/15] CIFS: Add support for direct I/O read
    Date
    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");
    +
    + 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;
    + 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) {
    + add_credits_and_wake_if(server, rdata->credits, 0);
    + kref_put(&rdata->refcount,
    + cifs_direct_readdata_release);
    + if (rc == -EAGAIN)
    + continue;
    + break;
    + }
    +
    + wait_for_completion(&rdata->done);
    + rc = rdata->result;
    + if (rc) {
    + kref_put(
    + &rdata->refcount,
    + cifs_direct_readdata_release);
    + if (rc == -EAGAIN)
    + continue;
    + break;
    + }
    +
    + 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;
    --
    2.7.4
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