virtio-console: Implement redirection for stdin/stdout/stderr

TODO: implement stderr here too!

This is done by creating a port for each of stdin/stdout/stderr,
Each of these ports is multidirectional but we only use one direction.
Port 0 must always be a console - this is implied by the specification.

Signed-off-by: Matej Hrica <[email protected]>

Author: mtjhrc

Cargo.lock

@@ -756,6 +756,68 @@ void clock_worker()
 }
 #endif
 
+int reopen_fd(int fd, char *path, int flags)
+{
+    int newfd = open(path,flags);
+    if (newfd < 0) {
+        printf("Failed to open '%s': %s\n", path,strerror(errno));
+        return -1;
+    }
+
+    close(fd);
+    if (dup2(newfd, fd) < 0) {
+        perror("dup2");
+        close(newfd);
+        return -1;
+    }
+    close(newfd);
+    return 0;
+}
+
+int setup_redirects()
+{
+    DIR *ports_dir = opendir("/sys/class/virtio-ports");
+    if (ports_dir == NULL) {
+        printf("Unable to open ports directory!\n");
+        return -4;
+    }
+
+    char path[2048];
+    char name_buf[1024];
+
+    struct dirent *entry = NULL;
+    while ((entry=readdir(ports_dir))) {
+        char* port_identifier = entry->d_name;
+        int result_len = snprintf(path, sizeof(path), "/sys/class/virtio-ports/%s/name", port_identifier);
+
+        // result was truncated
+        if (result_len > sizeof(name_buf) - 1) {
+            printf("Path buffer too small");
+            return -1;
+        }
+
+        FILE *port_name_file = fopen(path, "r");
+        if (port_name_file == NULL) {
+            continue;
+        }
+
+        char *port_name = fgets(name_buf, sizeof(name_buf), port_name_file);
+        fclose(port_name_file);
+
+        if (port_name != NULL && strcmp(port_name, "krun-stdin\n") == 0) {
+            // if previous snprintf didn't fail, this one cannot fail either
+            snprintf(path, sizeof(path), "/dev/%s", port_identifier);
+            reopen_fd(STDIN_FILENO, path, O_RDONLY);
+        }else if (port_name != NULL && strcmp(port_name, "krun-stdout\n") == 0) {
+             snprintf(path, sizeof(path), "/dev/%s", port_identifier);
+             reopen_fd(STDOUT_FILENO, path, O_WRONLY);
+        }
+    }
+
+    closedir(ports_dir);
+    return 0;
+}
+
 int main(int argc, char **argv)
 {
 	struct ifreq ifr;
@@ -848,6 +910,10 @@ int main(int argc, char **argv)
 	}
 #endif
 
+    if (setup_redirects() < 0) {
+       exit(-4);
+    }
+
 	if (execvp(exec_argv[0], exec_argv) < 0) {
 		printf("Couldn't execute '%s' inside the vm: %s\n", exec_argv[0], strerror(errno));
 		exit(-3);

init/init.c

@@ -15,7 +15,7 @@ crossbeam-channel = "0.5"
 env_logger = "0.9.0"
 libc = ">=0.2.39"
 log = "0.4.0"
-nix = "0.24.1"
+nix = { version = "0.24.1", features = ["poll"] }
 rand = "0.8.5"
 vm-memory = { version = ">=0.13", features = ["backend-mmap"] }
 

src/devices/Cargo.toml

@@ -7,7 +7,8 @@ use utils::eventfd::EventFd;
 use vm_memory::{ByteValued, GuestMemoryMmap};
 
 use crate::virtio::console::defs::control_event::{
-    VIRTIO_CONSOLE_CONSOLE_PORT, VIRTIO_CONSOLE_PORT_ADD, VIRTIO_CONSOLE_RESIZE,
+    VIRTIO_CONSOLE_CONSOLE_PORT, VIRTIO_CONSOLE_PORT_ADD, VIRTIO_CONSOLE_PORT_NAME,
+    VIRTIO_CONSOLE_PORT_OPEN, VIRTIO_CONSOLE_RESIZE,
 };
 
 #[derive(Copy, Clone, Debug, Default)]
@@ -99,6 +100,31 @@ impl ConsoleControl {
         })
     }
 
+    pub fn port_open(&self, port_id: u32, open: bool) {
+        self.push_msg(VirtioConsoleControl {
+            id: port_id,
+            event: VIRTIO_CONSOLE_PORT_OPEN,
+            value: open as u16,
+        })
+    }
+
+    pub fn port_name(&self, port_id: u32, name: &str) {
+        let mut buf: Vec<u8> = Vec::new();
+
+        buf.extend_from_slice(
+            VirtioConsoleControl {
+                id: port_id,
+                event: VIRTIO_CONSOLE_PORT_NAME,
+                value: 1, // Unspecified/unused in the spec, lets use the same value as QEMU.
+            }
+            .as_slice(),
+        );
+
+        // The spec says the name shouldn't be NUL terminated.
+        buf.extend(name.as_bytes());
+        self.push_vec(buf)
+    }
+
     pub fn queue_pop(&self) -> Option<Payload> {
         let mut queue = self.queue.lock().expect("Poisoned lock");
         queue.pop_front()