Is there a good way to detect a stale NFS mount

Question

I have a procedure I want to initiate only if several tests complete successfully.

One test I need is that all of my NFS mounts are alive and well.

Can I do

Answer 1

Writing a C program that checks for ESTALE is a good option if you don't mind waiting for the command to finish because of the stale file system. If you want to implement a "timeout" option the best way I've found to implement it (in a C program) is to fork a child process that tries to open the file. You then check if the child process has finished reading a file successfully in the filesystem within an allocated amount of time.

Here is a small proof of concept C program to do this:

#include 
#include 
#include 
#include 
#include 
#include 
#include 


void readFile();
void waitForChild(int pid);


int main(int argc, char *argv[])
{
  int pid;

  pid = fork();

  if(pid == 0) {
    // Child process.
    readFile();
  }
  else if(pid > 0) {
    // Parent process.
    waitForChild(pid);
  }
  else {
    // Error
    perror("Fork");
    exit(1);
  }

  return 0;
}

void waitForChild(int child_pid)
{
  int timeout = 2; // 2 seconds timeout.
  int status;
  int pid;

  while(timeout != 0) {
    pid = waitpid(child_pid, &status, WNOHANG);
    if(pid == 0) {
      // Still waiting for a child.
      sleep(1);
      timeout--;
    }
    else if(pid == -1) {
      // Error
      perror("waitpid()");
      exit(1);
    }
    else {
      // The child exited.
      if(WIFEXITED(status)) {
        // Child was able to call exit().
        if(WEXITSTATUS(status) == 0) {
          printf("File read successfully!\n");
          return;
        }
      }
      printf("File NOT read successfully.\n");
      return;
    }
  }

  // The child did not finish and the timeout was hit.
  kill(child_pid, 9);
  printf("Timeout reading the file!\n");
}

void readFile()
{
  int fd;

  fd = open("/path/to/a/file", O_RDWR);
  if(fd == -1) {
    // Error
    perror("open()");
    exit(1);
  }
  else {
    close(fd);
    exit(0);
  }
}