ftdev: provide a callback to test whether a device can be opened

This is useful to deny opening per-cpu buffers if a CPU is not online.

2 files changed, 11 insertions, 2 deletions

diff --git a/include/litmus/ftdev.h b/include/litmus/ftdev.h
index 8df916d1fc..7697b46166 100644
--- a/include/litmus/ftdev.h
+++ b/include/litmus/ftdev.h
@@ -13,9 +13,13 @@
 
 struct ftdev;
 
+/* return 0 if buffer can be opened, otherwise -$REASON */
+typedef int  (*ftdev_can_open_t)(struct ftdev* dev, unsigned int buf_no);
+/* return 0 on success, otherwise -$REASON */
 typedef int  (*ftdev_alloc_t)(struct ftdev* dev, unsigned int buf_no);
 typedef void (*ftdev_free_t)(struct ftdev* dev, unsigned int buf_no);
 
+
 struct ftdev_event;
 
 struct ftdev_minor {
@@ -33,6 +37,7 @@ struct ftdev {
         unsigned int            minor_cnt;
         ftdev_alloc_t           alloc;
         ftdev_free_t            free;
+        ftdev_can_open_t        can_open;
 };
 
 struct ft_buffer* alloc_ft_buffer(unsigned int count, size_t size);
diff --git a/litmus/ftdev.c b/litmus/ftdev.c
index fe3005db6d..20402c476f 100644
--- a/litmus/ftdev.c
+++ b/litmus/ftdev.c
@@ -106,6 +106,9 @@ static int ftdev_open(struct inode *in, struct file *filp)
                 err = -ENODEV;
                 goto out;
         }
+        if (ftdev->can_open && (err = ftdev->can_open(ftdev, buf_idx)))
+                goto out;
+                
         ftdm = ftdev->minor + buf_idx;
         filp->private_data = ftdm;
 
@@ -313,8 +316,9 @@ void ftdev_init(struct ftdev* ftdev, struct module* owner)
                 ftdev->minor[i].buf     = NULL;
                 ftdev->minor[i].events  = NULL;
         }
-        ftdev->alloc = NULL;
-        ftdev->free  = NULL;
+        ftdev->alloc    = NULL;
+        ftdev->free     = NULL;
+        ftdev->can_open = NULL;
 }
 
 int register_ftdev(struct ftdev* ftdev, const char* name, int major)