unix: Use flock to ensure exclusive access #266
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
sirhcel
reviewed
May 16, 2025
| @@ -130,6 +167,9 @@ impl TTYPort { | |||
| // other applications that may have an exclusive port lock. | |||
| ioctl::tiocexcl(fd.0)?; | |||
|
|
|||
| // Also use flock to lock the port | |||
| flock_exclusive(fd.0)?; | |||
There was a problem hiding this comment.
After sleeping over it: Shouldn't we make this a "all or nothing" operation and attempt to gracefully retreat from this situation an not leave a port locked in the one way or the other?
There was a problem hiding this comment.
Yes, but that is what should be happening already. If the flock fails, then an error will be returned, and the serial port is not opened.
If the call to ioctl::tiocexcl fails, then we never get to the point where flock is called.
The lock placed by flock will be removed automatically when the file descriptor is closed, according to its man page.
There was a problem hiding this comment.
Right. I should add a note on that for future me.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Some applications, e.g. picocom, use
flockto ensure exclusive access to the serial port, but don't seem to use thetiocexclioctl. This means that, without usingflock, it is currently possible to connect to a port using picocom first, and then connect using this crate. This leads to problem where not all data is received by the Rust application.To avoid this,
flockcan be used to acquire an advisory lock on the port. This will prevent this crate from opening the port when it has already been opened by picocom. Note that the lock is only advisory, meaning that this requires collaboration between applications.Fixes #265.