IB/uverbs: New macro to set pointers to NULL if length is 0 in INIT_UDATA()

Trying to have a ternary operator to choose between NULL (or 0) and the
real pointer value in invocations leads to an impossible choice between
a sparse error about a literal 0 used as a NULL pointer, and a gcc
warning about "pointer/integer type mismatch in conditional expression."

Rather than clutter the source with more casts, move the ternary
operator into a new INIT_UDATA_BUF_OR_NULL() macro, which makes it
easier to use and simplifies its callers.

Reported-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

2 files changed, 16 insertions, 11 deletions

diff --git a/drivers/infiniband/core/uverbs.h b/drivers/infiniband/core/uverbs.h
index 9879568aed8c..a283274a5a09 100644
--- a/drivers/infiniband/core/uverbs.h
+++ b/drivers/infiniband/core/uverbs.h
@@ -55,6 +55,14 @@
                 (udata)->outlen = (olen);                               \
         } while (0)
 
+#define INIT_UDATA_BUF_OR_NULL(udata, ibuf, obuf, ilen, olen)                   \
+        do {                                                                    \
+                (udata)->inbuf  = (ilen) ? (const void __user *) (ibuf) : NULL; \
+                (udata)->outbuf = (olen) ? (void __user *) (obuf) : NULL;       \
+                (udata)->inlen  = (ilen);                                       \
+                (udata)->outlen = (olen);                                       \
+        } while (0)
+
 /*
  * Our lifetime rules for these structs are the following:
  *
diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index 34386943ebcf..699463bbfd2d 100644
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -676,17 +676,14 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
                                 return -EINVAL;
                 }
 
-                INIT_UDATA(&ucore,
-                           (hdr.in_words) ? buf : 0,
-                           (unsigned long)ex_hdr.response,
-                           hdr.in_words * 8,
-                           hdr.out_words * 8);
-
-                INIT_UDATA(&uhw,
-                           (ex_hdr.provider_in_words) ? buf + ucore.inlen : 0,
-                           (ex_hdr.provider_out_words) ? (unsigned long)ex_hdr.response + ucore.outlen : 0,
-                           ex_hdr.provider_in_words * 8,
-                           ex_hdr.provider_out_words * 8);
+                INIT_UDATA_BUF_OR_NULL(&ucore, buf, (unsigned long) ex_hdr.response,
+                                       hdr.in_words * 8, hdr.out_words * 8);
+
+                INIT_UDATA_BUF_OR_NULL(&uhw,
+                                       buf + ucore.inlen,
+                                       (unsigned long) ex_hdr.response + ucore.outlen,
+                                       ex_hdr.provider_in_words * 8,
+                                       ex_hdr.provider_out_words * 8);
 
                 err = uverbs_ex_cmd_table[command](file,
                                                    &ucore,