block: fix partial read() of /proc/{partitions,diskstats}

The proc files get truncated if they do not fit into the buffer with
a single read(). We need to move the seq_file index from the callback
of class_find_device() to the caller of class_find_device(), to keep
its value across multiple invocations of the callback.

Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 8 insertions, 6 deletions

diff --git a/block/genhd.c b/block/genhd.c
index c13cc77291af..f34befc54847 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -293,25 +293,26 @@ void __init printk_all_partitions(void)
 /* iterator */
 static int find_start(struct device *dev, void *data)
 {
-        loff_t k = *(loff_t *)data;
+        loff_t *k = data;
 
         if (dev->type != &disk_type)
                 return 0;
-        if (!k--)
+        if (!*k)
                 return 1;
+        (*k)--;
         return 0;
 }
 
 static void *part_start(struct seq_file *part, loff_t *pos)
 {
         struct device *dev;
-        loff_t n = *pos;
+        loff_t k = *pos;
 
-        if (!n)
+        if (!k)
                 seq_puts(part, "major minor  #blocks  name\n\n");
 
         mutex_lock(&block_class_lock);
-        dev = class_find_device(&block_class, NULL, (void *)pos, find_start);
+        dev = class_find_device(&block_class, NULL, &k, find_start);
         if (dev)
                 return dev_to_disk(dev);
         return NULL;
@@ -568,9 +569,10 @@ static struct device_type disk_type = {
 static void *diskstats_start(struct seq_file *part, loff_t *pos)
 {
         struct device *dev;
+        loff_t k = *pos;
 
         mutex_lock(&block_class_lock);
-        dev = class_find_device(&block_class, NULL, (void *)pos, find_start);
+        dev = class_find_device(&block_class, NULL, &k, find_start);
         if (dev)
                 return dev_to_disk(dev);
         return NULL;