[PATCH] virtiofsd: Fix side-effect in assert()

[Greg Kurz <groug@kaod.org>]

It is bad practice to put an expression with a side-effect in
assert() because the side-effect won't happen if the code is
compiled with -DNDEBUG.

Use an intermediate variable. Consolidate this in an macro to
have proper line numbers when the assertion is hit.

virtiofsd: ../../tools/virtiofsd/passthrough_ll.c:2797: lo_getxattr:
 Assertion `fchdir_res == 0' failed.
Aborted

  2796          /* fchdir should not fail here */
=>2797          FCHDIR_NOFAIL(lo->proc_self_fd);
  2798          ret = getxattr(procname, name, value, size);
  2799          FCHDIR_NOFAIL(lo->root.fd);

Fixes: bdfd66788349 ("virtiofsd: Fix xattr operations")
Cc: misono.tomohiro@jp.fujitsu.com
Signed-off-by: Greg Kurz <groug@kaod.org>
---
 tools/virtiofsd/passthrough_ll.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 1553d2ef454f..6592f96f685e 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -2723,6 +2723,11 @@ static int xattr_map_server(const struct lo_data *lo, const char *server_name,
     return -ENODATA;
 }
 
+#define FCHDIR_NOFAIL(fd) do {                         \
+        int fchdir_res = fchdir(fd);                   \
+        assert(fchdir_res == 0);                       \
+    } while (0)
+
 static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name,
                         size_t size)
 {
@@ -2789,9 +2794,9 @@ static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name,
         ret = fgetxattr(fd, name, value, size);
     } else {
         /* fchdir should not fail here */
-        assert(fchdir(lo->proc_self_fd) == 0);
+        FCHDIR_NOFAIL(lo->proc_self_fd);
         ret = getxattr(procname, name, value, size);
-        assert(fchdir(lo->root.fd) == 0);
+        FCHDIR_NOFAIL(lo->root.fd);
     }
 
     if (ret == -1) {
@@ -2864,9 +2869,9 @@ static void lo_listxattr(fuse_req_t req, fuse_ino_t ino, size_t size)
         ret = flistxattr(fd, value, size);
     } else {
         /* fchdir should not fail here */
-        assert(fchdir(lo->proc_self_fd) == 0);
+        FCHDIR_NOFAIL(lo->proc_self_fd);
         ret = listxattr(procname, value, size);
-        assert(fchdir(lo->root.fd) == 0);
+        FCHDIR_NOFAIL(lo->root.fd);
     }
 
     if (ret == -1) {
@@ -3000,9 +3005,9 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name,
         ret = fsetxattr(fd, name, value, size, flags);
     } else {
         /* fchdir should not fail here */
-        assert(fchdir(lo->proc_self_fd) == 0);
+        FCHDIR_NOFAIL(lo->proc_self_fd);
         ret = setxattr(procname, name, value, size, flags);
-        assert(fchdir(lo->root.fd) == 0);
+        FCHDIR_NOFAIL(lo->root.fd);
     }
 
     saverr = ret == -1 ? errno : 0;
@@ -3066,9 +3071,9 @@ static void lo_removexattr(fuse_req_t req, fuse_ino_t ino, const char *in_name)
         ret = fremovexattr(fd, name);
     } else {
         /* fchdir should not fail here */
-        assert(fchdir(lo->proc_self_fd) == 0);
+        FCHDIR_NOFAIL(lo->proc_self_fd);
         ret = removexattr(procname, name);
-        assert(fchdir(lo->root.fd) == 0);
+        FCHDIR_NOFAIL(lo->root.fd);
     }
 
     saverr = ret == -1 ? errno : 0;
-- 
2.26.3