simplify faccessat AT_EACCESS path and eliminate resource dependence

now that we're waiting for the exit status of the child process, the
result can be conveyed in the exit status rather than via a pipe.
since the error value might not fit in 7 bits, a table is used to
translate possible meaningful error values to small integers.

diff --git a/src/unistd/faccessat.c b/src/unistd/faccessat.c
index 76bbd4c..3347895 100644 (file)
--- a/src/unistd/faccessat.c
+++ b/src/unistd/faccessat.c
@@ -1,5 +1,6 @@
 #include <unistd.h>
 #include <fcntl.h>
+#include <errno.h>
 #include <sys/wait.h>
 #include "syscall.h"
 #include "pthread_impl.h"
@@ -8,19 +9,26 @@ struct ctx {
        int fd;
        const char *filename;
        int amode;
-       int p;
+};
+
+static const int errors[] = {
+       0, -EACCES, -ELOOP, -ENAMETOOLONG, -ENOENT, -ENOTDIR,
+       -EROFS, -EBADF, -EINVAL, -ETXTBSY,
+       -EFAULT, -EIO, -ENOMEM,
+       -EBUSY
 };
 
 static int checker(void *p)
 {
        struct ctx *c = p;
        int ret;
+       int i;
        if (__syscall(SYS_setregid, __syscall(SYS_getegid), -1)
            || __syscall(SYS_setreuid, __syscall(SYS_geteuid), -1))
                __syscall(SYS_exit, 1);
        ret = __syscall(SYS_faccessat, c->fd, c->filename, c->amode, 0);
-       __syscall(SYS_write, c->p, &ret, sizeof ret);
-       return 0;
+       for (i=0; i < sizeof errors/sizeof *errors - 1 && ret!=errors[i]; i++);
+       return i;
 }
 
 int faccessat(int fd, const char *filename, int amode, int flag)
@@ -34,21 +42,20 @@ int faccessat(int fd, const char *filename, int amode, int flag)
        char stack[1024];
        sigset_t set;
        pid_t pid;
-       int status;
-       int ret, p[2];
-
-       if (pipe2(p, O_CLOEXEC)) return __syscall_ret(-EBUSY);
-       struct ctx c = { .fd = fd, .filename = filename, .amode = amode, .p = p[1] };
+       int ret = -EBUSY;
+       struct ctx c = { .fd = fd, .filename = filename, .amode = amode };
 
        __block_all_sigs(&set);
        
        pid = __clone(checker, stack+sizeof stack, 0, &c);
-       __syscall(SYS_close, p[1]);
-
-       if (pid<0 || __syscall(SYS_read, p[0], &ret, sizeof ret) != sizeof(ret))
-               ret = -EBUSY;
-       __syscall(SYS_close, p[0]);
-       __syscall(SYS_wait4, pid, &status, __WCLONE, 0);
+       if (pid > 0) {
+               int status;
+               do {
+                       __syscall(SYS_wait4, pid, &status, __WCLONE, 0);
+               } while (!WIFEXITED(status) && !WIFSIGNALED(status));
+               if (WIFEXITED(status))
+                       ret = errors[WEXITSTATUS(status)];
+       }
 
        __restore_sigs(&set);