Re: [PATCH] vfio-pci: PCI hot reset interface

[Al Viro <viro@ZenIV.linux.org.uk>]

On Wed, Aug 14, 2013 at 04:42:14PM -0600, Bjorn Helgaas wrote:
> [+cc Al, linux-fsdevel for fdget/fdput usage]

fdget/fdput use looks sane, the only thing is that I would rather
have an explicit include of linux/file.h instead of relying upon
linux/eventfd.h pulling it.  Incidentally, there are only 5 files
that include the latter without an explicit include of the former -
drivers/vfio/pci/vfio_pci.c, drivers/vhost/scsi.c, kernel/cgroup.c,
mm/memcontrol.c and mm/vmpressure.c.  And only kernel/cgroup.c (and,
with this patch, vfio_pci.c) really wants anything from linux/file.h,
so I'd rather kill that indirect include in eventfd.h and slapped
an explicit include of file.h in these two files...

BTW, most of the eventfd_fget() users might as well be using fget()
(or fdget(), for that matter).  They tend to be immediately followed
by eventfd_ctx_fileget(), which repeats the "is that an eventfd file?"
check anyway.

Completely untested patch below does that to kernel/cgroup.c; Tejun,
Davide - do you have any objections against the following?

Kill indirect include of file.h from eventfd.h, use fdget() in cgroup.c

kernel/cgroup.c is the only place in the tree that relies on eventfd.h
pulling file.h; move that include there.  Switch from eventfd_fget()/fput()
to fdget()/fdput(), while we are at it - eventfd_ctx_fileget() will fail
on non-eventfd descriptors just fine, no need to do that check twice...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h
index cf5d2af..ff0b981 100644
--- a/include/linux/eventfd.h
+++ b/include/linux/eventfd.h
@@ -9,7 +9,6 @@
 #define _LINUX_EVENTFD_H
 
 #include <linux/fcntl.h>
-#include <linux/file.h>
 #include <linux/wait.h>
 
 /*
@@ -26,6 +25,8 @@
 #define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK)
 #define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE)
 
+struct file;
+
 #ifdef CONFIG_EVENTFD
 
 struct file *eventfd_file_create(unsigned int count, int flags);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 781845a..f88ecaf 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -60,6 +60,7 @@
 #include <linux/poll.h>
 #include <linux/flex_array.h> /* used in cgroup_attach_task */
 #include <linux/kthread.h>
+#include <linux/file.h>
 
 #include <linux/atomic.h>
 
@@ -3969,8 +3970,8 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
 	struct cgroup_event *event = NULL;
 	struct cgroup *cgrp_cfile;
 	unsigned int efd, cfd;
-	struct file *efile = NULL;
-	struct file *cfile = NULL;
+	struct fd efile;
+	struct fd cfile;
 	char *endp;
 	int ret;
 
@@ -3993,31 +3994,31 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
 	init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
 	INIT_WORK(&event->remove, cgroup_event_remove);
 
-	efile = eventfd_fget(efd);
-	if (IS_ERR(efile)) {
-		ret = PTR_ERR(efile);
-		goto fail;
+	efile = fdget(efd);
+	if (!efile.file) {
+		ret = -EBADF;
+		goto fail1;
 	}
 
-	event->eventfd = eventfd_ctx_fileget(efile);
+	event->eventfd = eventfd_ctx_fileget(efile.file);
 	if (IS_ERR(event->eventfd)) {
 		ret = PTR_ERR(event->eventfd);
-		goto fail;
+		goto fail2;
 	}
 
-	cfile = fget(cfd);
-	if (!cfile) {
+	cfile = fdget(cfd);
+	if (!cfile.file) {
 		ret = -EBADF;
-		goto fail;
+		goto fail3;
 	}
 
 	/* the process need read permission on control file */
 	/* AV: shouldn't we check that it's been opened for read instead? */
-	ret = inode_permission(file_inode(cfile), MAY_READ);
+	ret = inode_permission(file_inode(cfile.file), MAY_READ);
 	if (ret < 0)
 		goto fail;
 
-	event->cft = __file_cft(cfile);
+	event->cft = __file_cft(cfile.file);
 	if (IS_ERR(event->cft)) {
 		ret = PTR_ERR(event->cft);
 		goto fail;
@@ -4027,7 +4028,7 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
 	 * The file to be monitored must be in the same cgroup as
 	 * cgroup.event_control is.
 	 */
-	cgrp_cfile = __d_cgrp(cfile->f_dentry->d_parent);
+	cgrp_cfile = __d_cgrp(cfile.file->f_dentry->d_parent);
 	if (cgrp_cfile != cgrp) {
 		ret = -EINVAL;
 		goto fail;
@@ -4043,7 +4044,7 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
 	if (ret)
 		goto fail;
 
-	efile->f_op->poll(efile, &event->pt);
+	efile.file->f_op->poll(efile.file, &event->pt);
 
 	/*
 	 * Events should be removed after rmdir of cgroup directory, but before
@@ -4056,21 +4057,18 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
 	list_add(&event->list, &cgrp->event_list);
 	spin_unlock(&cgrp->event_list_lock);
 
-	fput(cfile);
-	fput(efile);
+	fdput(cfile);
+	fdput(efile);
 
 	return 0;
 
 fail:
-	if (cfile)
-		fput(cfile);
-
-	if (event && event->eventfd && !IS_ERR(event->eventfd))
-		eventfd_ctx_put(event->eventfd);
-
-	if (!IS_ERR_OR_NULL(efile))
-		fput(efile);
-
+	fdput(cfile);
+fail3:
+	eventfd_ctx_put(event->eventfd);
+fail2:
+	fdput(efile);
+fail1:
 	kfree(event);
 
 	return ret;