[PATCH] scsi: osst: Use struct_size() in kzalloc()

[Gustavo A. R. Silva]

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct osst_buffer {
  ...
  struct scatterlist sg[1];    /* MUST BE last item                             
  */
} ;

i = sizeof(struct osst_buffer) + (osst_max_sg_segs - 1) * sizeof(struct 
scatterlist);
instance = kzalloc(i, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = kzalloc(struct_size(instance, sg, count), GFP_KERNEL);

Notice that, in this case, variable i is not necessary, hence it
is removed.

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gust...@embeddedor.com>
---
 drivers/scsi/osst.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/scsi/osst.c b/drivers/scsi/osst.c
index 815bb4097c1b..a11455a7e6bf 100644
--- a/drivers/scsi/osst.c
+++ b/drivers/scsi/osst.c
@@ -5307,7 +5307,6 @@ static long osst_compat_ioctl(struct file * file, 
unsigned int cmd_in, unsigned
 /* Try to allocate a new tape buffer skeleton. Caller must not hold 
os_scsi_tapes_lock */
 static struct osst_buffer * new_tape_buffer( int from_initialization, int 
need_dma, int max_sg )
 {
-       int i;
        gfp_t priority;
        struct osst_buffer *tb;
 
@@ -5316,8 +5315,7 @@ static struct osst_buffer * new_tape_buffer( int 
from_initialization, int need_d
        else
                priority = GFP_KERNEL;
 
-       i = sizeof(struct osst_buffer) + (osst_max_sg_segs - 1) * sizeof(struct 
scatterlist);
-       tb = kzalloc(i, priority);
+       tb = kzalloc(struct_size(tb, sg, osst_max_sg_segs - 1), priority);
        if (!tb) {
                printk(KERN_NOTICE "osst :I: Can't allocate new tape 
buffer.\n");
                return NULL;
-- 
2.21.0