provide an initializer for "struct object_info"

An all-zero initializer is fine for this struct, but because
the first element is a pointer, call sites need to know to
use "NULL" instead of "0". Otherwise some static checkers
like "sparse" will complain; see d099b71 (Fix some sparse
warnings, 2013-07-18) for example.  So let's provide an
initializer to make this easier to get right.

But let's also comment that memset() to zero is explicitly
OK[1]. One of the callers embeds object_info in another
struct which is initialized via memset (expand_data in
builtin/cat-file.c). Since our subset of C doesn't allow
assignment from a compound literal, handling this in any
other way is awkward, so we'd like to keep the ability to
initialize by memset(). By documenting this property, it
should make anybody who wants to change the initializer
think twice before doing so.

There's one other caller of interest. In parse_sha1_header(),
we did not initialize the struct fully in the first place.
This turned out not to be a bug because the sub-function it
calls does not look at any other fields except the ones we
did initialize. But that assumption might not hold in the
future, so it's a dangerous construct. This patch switches
it to initializing the whole struct, which protects us
against unexpected reads of the other fields.

[1] Obviously using memset() to initialize a pointer
violates the C standard, but we long ago decided that it
was an acceptable tradeoff in the real world.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 618103fdeeb7f7b35911ebd12d0d811cc4a5297a..8e579980b63888383835140608ef444e92eab8f2 100644 (file)
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -28,7 +28,7 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name,
        char *buf;
        unsigned long size;
        struct object_context obj_context;
-       struct object_info oi = {NULL};
+       struct object_info oi = OBJECT_INFO_INIT;
        struct strbuf sb = STRBUF_INIT;
        unsigned flags = LOOKUP_REPLACE_OBJECT;
 
@@ -378,8 +378,7 @@ static int batch_objects(struct batch_options *opt)
        data.mark_query = 0;
 
        if (opt->all_objects) {
-               struct object_info empty;
-               memset(&empty, 0, sizeof(empty));
+               struct object_info empty = OBJECT_INFO_INIT;
                if (!memcmp(&data.info, &empty, sizeof(empty)))
                        data.skip_object_info = 1;
        }

diff --git a/cache.h b/cache.h
index 40671d160a0a31a475d7f317966798d5dea248b7..1fa2871b4346914406b858fc23ade2781cb9441e 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -1542,6 +1542,13 @@ struct object_info {
                } packed;
        } u;
 };
+
+/*
+ * Initializer for a "struct object_info" that wants no items. You may
+ * also memset() the memory to all-zeroes.
+ */
+#define OBJECT_INFO_INIT {NULL}
+
 extern int sha1_object_info_extended(const unsigned char *, struct object_info *, unsigned flags);
 
 /* Dumb servers support */

diff --git a/sha1_file.c b/sha1_file.c
index 4eb3318ae0c189106f43ac56ae472f8af66cb14f..090cedb8eb8eb245b1dced597e8c40801d1757d1 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1730,11 +1730,9 @@ static int parse_sha1_header_extended(const char *hdr, struct object_info *oi,
 
 int parse_sha1_header(const char *hdr, unsigned long *sizep)
 {
-       struct object_info oi;
+       struct object_info oi = OBJECT_INFO_INIT;
 
        oi.sizep = sizep;
-       oi.typename = NULL;
-       oi.typep = NULL;
        return parse_sha1_header_extended(hdr, &oi, LOOKUP_REPLACE_OBJECT);
 }
 
@@ -2738,7 +2736,7 @@ int sha1_object_info_extended(const unsigned char *sha1, struct object_info *oi,
 int sha1_object_info(const unsigned char *sha1, unsigned long *sizep)
 {
        enum object_type type;
-       struct object_info oi = {NULL};
+       struct object_info oi = OBJECT_INFO_INIT;
 
        oi.typep = &type;
        oi.sizep = sizep;

diff --git a/streaming.c b/streaming.c
index 811fcc24d2a8ba56c233ae4e37b7acac29a4a0d8..431254ba416ce8e48f71f8f85a1c70c2a56c7090 100644 (file)
--- a/streaming.c
+++ b/streaming.c
@@ -135,7 +135,7 @@ struct git_istream *open_istream(const unsigned char *sha1,
                                 struct stream_filter *filter)
 {
        struct git_istream *st;
-       struct object_info oi = {NULL};
+       struct object_info oi = OBJECT_INFO_INIT;
        const unsigned char *real = lookup_replace_object(sha1);
        enum input_source src = istream_source(real, type, &oi);