kernel+libc+init: Add a way to modify the system hostname

apps/init.cpp

@@ -199,6 +199,20 @@ static Result<void> start_services()
     return {};
 }
 
+static Result<void> set_hostname()
+{
+    auto file = TRY(os::File::open("/etc/hostname", os::File::ReadOnly));
+
+    auto hostname = TRY(file->read_line());
+    hostname.trim("\n");
+
+    if (sethostname(hostname.chars(), hostname.length()) < 0) return {};
+
+    fprintf(g_init_log, "[init] successfully set system hostname to '%s'\n", hostname.chars());
+
+    return {};
+}
+
 int main()
 {
     if (getpid() != 1)
@@ -218,6 +232,8 @@ int main()
     g_init_log = fopen("/init.log", "w+");
     fcntl(fileno(g_init_log), F_SETFD, FD_CLOEXEC);
 
+    set_hostname();
+
     start_services();
 
     while (1)

initrd/etc/hostname

@@ -0,0 +1 @@
+lunar

kernel/src/main.cpp

@@ -19,6 +19,8 @@
 #include <luna/Result.h>
 #include <luna/Units.h>
 
+extern void set_host_name(StringView);
+
 void reap_thread()
 {
     while (true)
@@ -37,6 +39,9 @@ Result<void> init()
 {
     kinfoln("Starting Moon %s, built on %s at %s", MOON_VERSION, __DATE__, __TIME__);
 
+    // Default hostname if nobody from userspace changes it
+    set_host_name("moon"_sv);
+
     kinfoln("Current platform: %s", CPU::platform_string());
     kinfoln("Current processor: %s", CPU::identify().value_or("(unknown)"));
 

kernel/src/sys/uname.cpp

@@ -1,8 +1,18 @@
 #include "arch/CPU.h"
+#include "config.h"
 #include "memory/MemoryManager.h"
 #include "sys/Syscall.h"
+#include "thread/Scheduler.h"
 #include <bits/struct_utsname.h>
 #include <luna/CString.h>
+#include <luna/StaticString.h>
+
+StaticString<_UTSNAME_LENGTH - 1> s_hostname;
+
+void set_host_name(StringView hostname)
+{
+    s_hostname.adopt(hostname.chars());
+}
 
 Result<u64> sys_uname(Registers*, SyscallArgs args)
 {
@@ -11,10 +21,10 @@ Result<u64> sys_uname(Registers*, SyscallArgs args)
     utsname result;
 
     strncpy(result.sysname, "moon", _UTSNAME_LENGTH);
-    strncpy(result.nodename, "lunar", _UTSNAME_LENGTH);
+    strncpy(result.nodename, s_hostname.chars(), _UTSNAME_LENGTH);
 
-    // FIXME: Hardcode these at build time instead of in code.
+    strncpy(result.release, MOON_VERSION, _UTSNAME_LENGTH);
-    strncpy(result.release, "0.1", _UTSNAME_LENGTH);
+    // FIXME: Hardcode this at build time instead of in code (should be the short commit hash).
     strncpy(result.version, "alpha", _UTSNAME_LENGTH);
 
     strncpy(result.machine, CPU::platform_string(), _UTSNAME_LENGTH);
@@ -23,3 +33,23 @@ Result<u64> sys_uname(Registers*, SyscallArgs args)
 
     return 0;
 }
+
+Result<u64> sys_sethostname(Registers*, SyscallArgs args)
+{
+    const char* buf = (const char*)args[0];
+    usize length = (usize)args[1];
+
+    Thread* current = Scheduler::current();
+    if (current->auth.euid != 0) return err(EPERM);
+
+    if (length >= _UTSNAME_LENGTH) return err(EINVAL);
+
+    char new_hostname[_UTSNAME_LENGTH];
+    memset(new_hostname, 0, _UTSNAME_LENGTH);
+
+    if (!MemoryManager::copy_from_user(buf, new_hostname, length)) return err(EFAULT);
+
+    s_hostname.adopt(new_hostname);
+
+    return 0;
+}

libc/include/unistd.h

@@ -109,6 +109,12 @@ extern "C"
     /* Remove a directory from the filesystem. */
     int rmdir(const char* path);
 
+    /* Get the current network hostname. */
+    int gethostname(char* buf, size_t len);
+
+    /* Set the current network hostname. */
+    int sethostname(const char* buf, size_t len);
+
 #ifdef __cplusplus
 }
 #endif

libc/src/unistd.cpp

@@ -8,6 +8,7 @@
 #include <stdlib.h>
 #include <sys/stat.h>
 #include <sys/syscall.h>
+#include <sys/utsname.h>
 #include <unistd.h>
 
 extern "C" long arch_invoke_syscall(long, uintptr_t, uintptr_t, uintptr_t, uintptr_t, uintptr_t);
@@ -313,4 +314,20 @@ extern "C"
         long rc = syscall(SYS_unlinkat, AT_FDCWD, path, AT_REMOVEDIR);
         __errno_return(rc, int);
     }
+
+    int gethostname(char* buf, size_t len)
+    {
+        struct utsname info;
+        if (uname(&info) < 0) return -1;
+
+        strlcpy(buf, info.nodename, len);
+
+        return 0;
+    }
+
+    int sethostname(const char* buf, size_t len)
+    {
+        long rc = syscall(SYS_sethostname, buf, len);
+        __errno_return(rc, int);
+    }
 }

libluna/include/luna/Syscall.h

@@ -4,7 +4,7 @@
     _e(exit) _e(clock_gettime) _e(mmap) _e(munmap) _e(usleep) _e(openat) _e(close) _e(read) _e(getpid) _e(write)       \
         _e(lseek) _e(mkdir) _e(execve) _e(mknod) _e(fork) _e(waitpid) _e(getppid) _e(fcntl) _e(getdents) _e(getuid)    \
             _e(geteuid) _e(getgid) _e(getegid) _e(setuid) _e(setgid) _e(seteuid) _e(setegid) _e(chmod) _e(chown)       \
-                _e(ioctl) _e(fstatat) _e(chdir) _e(getcwd) _e(unlinkat) _e(uname)
+                _e(ioctl) _e(fstatat) _e(chdir) _e(getcwd) _e(unlinkat) _e(uname) _e(sethostname)
 
 enum Syscalls
 {