block: Retry locking when interrupted by EINTR

Acquiring an image lock can be interrupted with EINTR. In this case, we
returned with an error. Instead, we now retry acquiring the lock.

Signed-off-by: Pascal Scholz <pascal.scholz@cyberus-technology.de>
On-behalf-of: SAP pascal.scholz@sap.com

block/src/io/fcntl.rs

@@ -201,20 +201,23 @@ pub fn try_acquire_lock<Fd: AsRawFd>(
 ) -> Result<(), LockError> {
     let flock = get_flock(lock_type, granularity);
 
-    let res = fcntl(file.as_raw_fd(), FcntlArg::F_OFD_SETLK(&flock));
-    match res {
-        0 => Ok(()),
-        -1 => {
-            let io_error = io::Error::last_os_error();
-            let errno = io_error.raw_os_error().unwrap();
-            match errno {
-                // See man page for error code:
-                // <https://man7.org/linux/man-pages/man2/fcntl.2.html>
-                libc::EAGAIN | libc::EACCES => Err(LockError::AlreadyLocked),
-                _ => Err(LockError::Io(io_error)),
+    loop {
+        let res = fcntl(file.as_raw_fd(), FcntlArg::F_OFD_SETLK(&flock));
+        match res {
+            0 => return Ok(()),
+            -1 => {
+                let io_error = io::Error::last_os_error();
+                let errno = io_error.raw_os_error().unwrap();
+                match errno {
+                    // See man page for error code:
+                    // <https://man7.org/linux/man-pages/man2/fcntl.2.html>
+                    libc::EAGAIN | libc::EACCES => return Err(LockError::AlreadyLocked),
+                    libc::EINTR => continue,
+                    _ => return Err(LockError::Io(io_error)),
+                }
             }
+            val => panic!("Unexpected return value from fcntl(): {val}"),
         }
-        val => panic!("Unexpected return value from fcntl(): {val}"),
     }
 }