[PATCH v3 1/4] osdep: Make qemu_madvise() to set errno in all cases

[Michal Privoznik]

The unspoken premise of qemu_madvise() is that errno is set on
error. And it is mostly the case except for posix_madvise() which
is documented to return either zero (on success) or a positive
error number. This means, we must set errno ourselves. And while
at it, make the function return a negative value on error, just
like other error paths do.

Signed-off-by: Michal Privoznik <mpriv...@redhat.com>
---
 util/osdep.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/util/osdep.c b/util/osdep.c
index e996c4744a..1345238a5c 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -57,7 +57,19 @@ int qemu_madvise(void *addr, size_t len, int advice)
 #if defined(CONFIG_MADVISE)
     return madvise(addr, len, advice);
 #elif defined(CONFIG_POSIX_MADVISE)
-    return posix_madvise(addr, len, advice);
+    /*
+     * On Darwin posix_madvise() has the same return semantics as
+     * plain madvise, i.e. errno is set and -1 is returned. Otherwise,
+     * a positive error number is returned.
+     */
+    int rc = posix_madvise(addr, len, advice);
+    if (rc) {
+        if (rc > 0) {
+            errno = rc;
+        }
+        return -1;
+    }
+    return 0;
 #else
     errno = EINVAL;
     return -1;
-- 
2.44.1