Re: [Patch v2 13/15] CIFS: Add support for direct I/O read
From: Tom Talpey
Date: Sat Jun 23 2018 - 22:39:53 EST
On 5/30/2018 3:48 PM, Long Li wrote:
From: Long Li <longli@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>
---
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;