[LibOS] Remove abspath check from *at() syscalls

This patch is a follow-up of
https://github.com/oscarlab/graphene/pull/671. With #671, absolute path
check is handled uniformly by __path_lookupat(). Now absolute path check
in each system call isn't needed, so we can remove it.

LibOS/shim/src/sys/shim_access.c

@@ -58,9 +58,6 @@ int shim_do_faccessat (int dfd, const char * filename, mode_t mode)
     if (test_user_string(filename))
         return -EFAULT;
 
-    if (*filename == '/')
-        return shim_do_access(filename, mode);
-
     struct shim_dentry * dir = NULL, * dent = NULL;
     int ret = 0;
 

LibOS/shim/src/sys/shim_fs.c

@@ -84,10 +84,6 @@ int shim_do_unlinkat (int dfd, const char * pathname, int flag)
     if (flag & ~AT_REMOVEDIR)
         return -EINVAL;
 
-    if (*pathname == '/')
-        return (flag & AT_REMOVEDIR) ? shim_do_rmdir(pathname) :
-               shim_do_unlink(pathname);
-
     struct shim_dentry * dir = NULL, * dent = NULL;
     int ret = 0;
 
@@ -142,9 +138,6 @@ int shim_do_mkdirat (int dfd, const char * pathname, int mode)
     if (test_user_string(pathname))
         return -EFAULT;
 
-    if (*pathname == '/')
-        return shim_do_mkdir(pathname, mode);
-
     struct shim_dentry * dir = NULL;
     int ret = 0;
 
@@ -239,9 +232,6 @@ int shim_do_fchmodat (int dfd, const char * filename, mode_t mode)
     if (test_user_string(filename))
         return -EFAULT;
 
-    if (*filename == '/')
-        return shim_do_chmod(filename, mode);
-
     struct shim_dentry * dir = NULL, * dent = NULL;
     int ret = 0;
 
@@ -313,15 +303,15 @@ int shim_do_fchownat (int dfd, const char * filename, uid_t uid, gid_t gid,
                       int flags)
 {
     __UNUSED(flags);
+    __UNUSED(uid);
+    __UNUSED(gid);
+
     if (!filename)
         return -EINVAL;
 
     if (test_user_string(filename))
         return -EFAULT;
 
-    if (*filename == '/')
-        return shim_do_chown(filename, uid, gid);
-
     struct shim_dentry * dir = NULL, * dent = NULL;
     int ret = 0;
 

LibOS/shim/src/sys/shim_open.c

@@ -134,9 +134,6 @@ int shim_do_openat (int dfd, const char * filename, int flags, int mode)
     if (!filename || test_user_string(filename))
         return -EFAULT;
 
-    if (*filename == '/')
-        return shim_do_open(filename, flags, mode);
-
     struct shim_dentry * dir = NULL;
     int ret = 0;