[PATCH 39/78] block: add an optional probe callback to major_names

[Christoph Hellwig <hch@xxxxxx>]

Add a callback to the major_names array that allows a driver to override
how to probe for dev_t that doesn't currently have a gendisk registered.
This will help separating the lookup of the gendisk by dev_t vs probe
action for a not currently registered dev_t.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
---
 block/genhd.c         | 21 ++++++++++++++++++---
 include/linux/genhd.h |  5 ++++-
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 8391e7d83a6920..dc8690bc281c16 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -399,6 +399,7 @@ static struct blk_major_name {
        struct blk_major_name *next;
        int major;
        char name[16];
+       void (*probe)(dev_t devt);
 } *major_names[BLKDEV_MAJOR_HASH_SIZE];
 static DEFINE_MUTEX(major_names_lock);
 
@@ -441,7 +442,8 @@ void blkdev_show(struct seq_file *seqf, off_t offset)
  * See Documentation/admin-guide/devices.txt for the list of allocated
  * major numbers.
  */
-int register_blkdev(unsigned int major, const char *name)
+int __register_blkdev(unsigned int major, const char *name,
+               void (*probe)(dev_t devt))
 {
        struct blk_major_name **n, *p;
        int index, ret = 0;
@@ -480,6 +482,7 @@ int register_blkdev(unsigned int major, const char *name)
        }
 
        p->major = major;
+       p->probe = probe;
        strlcpy(p->name, name, sizeof(p->name));
        p->next = NULL;
        index = major_to_index(major);
@@ -502,8 +505,7 @@ int register_blkdev(unsigned int major, const char *name)
        mutex_unlock(&major_names_lock);
        return ret;
 }
-
-EXPORT_SYMBOL(register_blkdev);
+EXPORT_SYMBOL(__register_blkdev);
 
 void unregister_blkdev(unsigned int major, const char *name)
 {
@@ -1030,6 +1032,19 @@ static ssize_t disk_badblocks_store(struct device *dev,
 
 static void request_gendisk_module(dev_t devt)
 {
+       unsigned int major = MAJOR(devt);
+       struct blk_major_name **n;
+
+       mutex_lock(&major_names_lock);
+       for (n = &major_names[major_to_index(major)]; *n; n = &(*n)->next) {
+               if ((*n)->major == major && (*n)->probe) {
+                       (*n)->probe(devt);
+                       mutex_unlock(&major_names_lock);
+                       return;
+               }
+       }
+       mutex_unlock(&major_names_lock);
+
        if (request_module("block-major-%d-%d", MAJOR(devt), MINOR(devt)) > 0)
                /* Make old-style 2.4 aliases work */
                request_module("block-major-%d", MAJOR(devt));
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 8427ad8bef520d..04f6a6bf577a90 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -366,7 +366,10 @@ extern void blk_unregister_region(dev_t devt, unsigned 
long range);
 
 #define alloc_disk(minors) alloc_disk_node(minors, NUMA_NO_NODE)
 
-int register_blkdev(unsigned int major, const char *name);
+int __register_blkdev(unsigned int major, const char *name,
+               void (*probe)(dev_t devt));
+#define register_blkdev(major, name) \
+       __register_blkdev(major, name, NULL)
 void unregister_blkdev(unsigned int major, const char *name);
 
 void revalidate_disk_size(struct gendisk *disk, bool verbose);
-- 
2.29.2