[PATCH v4 06/11] 9p: darwin: Move XATTR_SIZE_MAX->P9_XATTR_SIZE_MAX

[Will Cohen <wwcohen@gmail.com>]

From: Keno Fischer <keno@juliacomputing.com>

Signed-off-by: Keno Fischer <keno@juliacomputing.com>
Signed-off-by: Michael Roitzsch <reactorcontrol@icloud.com>

Because XATTR_SIZE_MAX is not defined on Darwin,
create a cross-platform P9_XATTR_SIZE_MAX instead.

[Will Cohen: - Adjust coding style
             - Lower XATTR_SIZE_MAX to 64k
             - Add explanatory context related to XATTR_SIZE_MAX]
[Fabian Franz: - Move XATTR_SIZE_MAX reference from 9p.c to
                 P9_XATTR_SIZE_MAX in 9p.h]
Signed-off-by: Will Cohen <wwcohen@gmail.com>
Signed-off-by: Fabian Franz <fabianfranz.oss@gmail.com>
---
 hw/9pfs/9p.c |  2 +-
 hw/9pfs/9p.h | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index f3b00d20a2..440bf5c9e5 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -3957,7 +3957,7 @@ static void coroutine_fn v9fs_xattrcreate(void *opaque)
         rflags |= XATTR_REPLACE;
     }
 
-    if (size > XATTR_SIZE_MAX) {
+    if (size > P9_XATTR_SIZE_MAX) {
         err = -E2BIG;
         goto out_nofid;
     }
diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
index 1567b67841..6a1856b4dc 100644
--- a/hw/9pfs/9p.h
+++ b/hw/9pfs/9p.h
@@ -479,4 +479,15 @@ struct V9fsTransport {
     void        (*push_and_notify)(V9fsPDU *pdu);
 };
 
+/*
+ * Darwin doesn't seem to define a maximum xattr size in its user
+ * space header, so manually configure it across platforms as 64k.
+ *
+ * Having no limit at all can lead to QEMU crashing during large g_malloc()
+ * calls. Because QEMU does not currently support macOS guests, the below
+ * preliminary solution only works due to its being a reflection of the limit of
+ * Linux guests.
+ */
+#define P9_XATTR_SIZE_MAX 65536
+
 #endif
-- 
2.32.0 (Apple Git-132)