Fix remote DNS (#898)

* dns remote resolv

* add fionread

* lint

Author: rennergade

scripts/lindfs-conf/etc/nsswitch.conf

@@ -1,3 +1,3 @@
 passwd: files
 group: files
-hosts: files
+hosts: files dns

scripts/lindfs-conf/etc/resolv.conf

@@ -0,0 +1,2 @@
+nameserver 8.8.8.8
+nameserver 8.8.4.4

src/rawposix/src/fs_calls.rs

@@ -9,10 +9,10 @@ use libc::c_void;
 use std::sync::Arc;
 use sysdefs::constants::err_const::{get_errno, handle_errno, syscall_error, Errno};
 use sysdefs::constants::fs_const::{
-    FIOASYNC, FIONBIO, F_GETLK64, F_SETLK64, F_SETLKW64, MAP_ANONYMOUS, MAP_FIXED, MAP_POPULATE,
-    MAP_PRIVATE, MAP_SHARED, O_CLOEXEC, PAGESHIFT, PAGESIZE, PROT_EXEC, PROT_NONE, PROT_READ,
-    PROT_WRITE, SHMMAX, SHMMIN, SHM_DEST, SHM_RDONLY, STDERR_FILENO, STDIN_FILENO, STDOUT_FILENO,
-    TIOCGWINSZ,
+    FIOASYNC, FIONBIO, FIONREAD, F_GETLK64, F_SETLK64, F_SETLKW64, MAP_ANONYMOUS, MAP_FIXED,
+    MAP_POPULATE, MAP_PRIVATE, MAP_SHARED, O_CLOEXEC, PAGESHIFT, PAGESIZE, PROT_EXEC, PROT_NONE,
+    PROT_READ, PROT_WRITE, SHMMAX, SHMMIN, SHM_DEST, SHM_RDONLY, STDERR_FILENO, STDIN_FILENO,
+    STDOUT_FILENO, TIOCGWINSZ,
 };
 
 use sysdefs::constants::lind_platform_const::{FDKIND_KERNEL, MAXFD, UNUSED_ARG, UNUSED_ID};
@@ -3857,9 +3857,9 @@ pub extern "C" fn ioctl_syscall(
         return ret;
     }
 
-    // Besides FIOCLEX, we only support FIONBIO, FIOASYNC, and TIOCGWINSZ right now.
+    // Besides FIOCLEX, we only support FIONBIO, FIOASYNC, FIONREAD, and TIOCGWINSZ right now.
     // Return error for unsupported requests.
-    if req != FIONBIO && req != FIOASYNC && req != TIOCGWINSZ {
+    if req != FIONBIO && req != FIOASYNC && req != FIONREAD && req != TIOCGWINSZ {
         lind_debug_panic("Lind unsupported ioctl request");
     }
 

src/sysdefs/src/constants/fs_const.rs

@@ -81,6 +81,7 @@ pub const F_NOTIFY: i32 = 1026;
 pub const FIONBIO: u32 = 21537;
 pub const FIOASYNC: u32 = 21586;
 pub const TIOCGWINSZ: u32 = 21523;
+pub const FIONREAD: u32 = 21531;
 
 //File types for open/stat etc.
 // Source: include/linux/stat.h

tests/unit-tests/networking_tests/deterministic/dns_resolve_test.c

@@ -0,0 +1,76 @@
+/* Test DNS resolution for external hostnames via getaddrinfo.
+ *
+ * Requires:
+ *   - /etc/nsswitch.conf with "hosts: files dns"
+ *   - /etc/resolv.conf with valid nameserver entries
+ *   - Network access to the configured nameserver
+ *
+ * Tests:
+ *   1. localhost resolves via /etc/hosts (files backend)
+ *   2. external hostname resolves via DNS (dns backend)
+ *   3. numeric IP resolves without DNS
+ */
+#include <stdio.h>
+#include <string.h>
+#include <netdb.h>
+#include <arpa/inet.h>
+#include <unistd.h>
+
+static int test_resolve(const char *host, int expect_success) {
+    struct addrinfo hints, *res;
+    memset(&hints, 0, sizeof(hints));
+    hints.ai_family = AF_INET;
+    hints.ai_socktype = SOCK_STREAM;
+
+    int ret = getaddrinfo(host, "80", &hints, &res);
+    if (expect_success && ret != 0) {
+        char buf[256];
+        int len = snprintf(buf, sizeof(buf),
+            "FAIL: getaddrinfo(\"%s\") failed: %s\n",
+            host, gai_strerror(ret));
+        write(2, buf, len);
+        return 1;
+    }
+    if (!expect_success && ret == 0) {
+        freeaddrinfo(res);
+        char buf[256];
+        int len = snprintf(buf, sizeof(buf),
+            "FAIL: getaddrinfo(\"%s\") succeeded but expected failure\n", host);
+        write(2, buf, len);
+        return 1;
+    }
+    if (expect_success) {
+        char addr_str[INET_ADDRSTRLEN];
+        struct sockaddr_in *sa = (struct sockaddr_in *)res->ai_addr;
+        inet_ntop(AF_INET, &sa->sin_addr, addr_str, sizeof(addr_str));
+        char buf[256];
+        int len = snprintf(buf, sizeof(buf),
+            "OK: %s -> %s\n", host, addr_str);
+        write(1, buf, len);
+        freeaddrinfo(res);
+    }
+    return 0;
+}
+
+int main(void) {
+    int failures = 0;
+
+    /* Test 1: localhost via /etc/hosts */
+    failures += test_resolve("localhost", 1);
+
+    /* Test 2: numeric IP (no DNS needed) */
+    failures += test_resolve("93.184.216.34", 1);
+
+    /* Test 3: external hostname via DNS */
+    failures += test_resolve("example.com", 1);
+
+    if (failures) {
+        char buf[64];
+        int len = snprintf(buf, sizeof(buf), "%d test(s) failed\n", failures);
+        write(2, buf, len);
+        return 1;
+    }
+
+    write(1, "done\n", 5);
+    return 0;
+}