drop direct use of stat syscalls in fchmodat

instead, use the fstatat/stat functions, so that the logic for which
syscalls are present and usable is all in fstatat.

this results in a slight increase in cost for old kernels on 32-bit
archs: now statx will be attempted first rather than just using the
legacy time32 syscalls, despite us not caring about timestamps.
however, it's not even clear that the legacy syscalls *should* succeed
if the timestamps are out of range; arguably they should fail with
EOVERFLOW. as such, paying a small cost here on old kernels seems
well-motivated.

with this change, fchmodat itself is no longer blocking ports to new
archs that lack the legacy syscalls.

diff --git a/src/stat/fchmodat.c b/src/stat/fchmodat.c
index 4ee00b0..bc58105 100644 (file)
--- a/src/stat/fchmodat.c
+++ b/src/stat/fchmodat.c
@@ -2,7 +2,6 @@
 #include <fcntl.h>
 #include <errno.h>
 #include "syscall.h"
-#include "kstat.h"
 
 int fchmodat(int fd, const char *path, mode_t mode, int flag)
 {
@@ -11,12 +10,12 @@ int fchmodat(int fd, const char *path, mode_t mode, int flag)
        if (flag != AT_SYMLINK_NOFOLLOW)
                return __syscall_ret(-EINVAL);
 
-       struct kstat st;
+       struct stat st;
        int ret, fd2;
        char proc[15+3*sizeof(int)];
 
-       if ((ret = __syscall(SYS_fstatat, fd, path, &st, flag)))
-               return __syscall_ret(ret);
+       if (fstatat(fd, path, &st, flag))
+               return -1;
        if (S_ISLNK(st.st_mode))
                return __syscall_ret(-EOPNOTSUPP);
 
@@ -27,12 +26,12 @@ int fchmodat(int fd, const char *path, mode_t mode, int flag)
        }
 
        __procfdname(proc, fd2);
-       ret = __syscall(SYS_fstatat, AT_FDCWD, proc, &st, 0);
+       ret = stat(proc, &st);
        if (!ret) {
-               if (S_ISLNK(st.st_mode)) ret = -EOPNOTSUPP;
-               else ret = __syscall(SYS_fchmodat, AT_FDCWD, proc, mode);
+               if (S_ISLNK(st.st_mode)) ret = __syscall_ret(-EOPNOTSUPP);
+               else ret = syscall(SYS_fchmodat, AT_FDCWD, proc, mode);
        }
 
        __syscall(SYS_close, fd2);
-       return __syscall_ret(ret);
+       return ret;
 }