Use pipe instead of 'sh -c' to spawn subprocesses #2580
Conversation
This file contains 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
Filling the whole command into 'sh -c' may hit length limit of single argument. For non-console subprocesses, use pipe to invoke sh instead.
digit-google
reviewed
Apr 7, 2025
| err = posix_spawn(&pid_, "/bin/sh", &action, &attr, | ||
| const_cast<char**>(spawned_args), environ); | ||
| if (err != 0) | ||
| Fatal("posix_spawn: %s", strerror(err)); | ||
|
|
||
| if (!use_console_) { | ||
| ssize_t written = write(input_pipe[1], command.c_str(), command.size()); |
There was a problem hiding this comment.
Does that work for large commands?
Most systems use a default pipe buffer size of 64 kiB, some even smaller (see https://github.com/afborchert/pipebuf) so this write() call will block infinitely if command.size() is larger than that (and the bug referenced by this PR talks about command sizes of 128 kiB).
Linux has fcntl(F_SETPIPE_SZ) to change that the pipe buffer size, but I am not aware of similar features on other systems. Even the Linux pipe manpage tsates that applications should not rely on a specific capacity.
It might be more portable and simple to write long commands to a file that is passed as the first argument to the shell instead. And that would also work for console processes too.
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Outdated suggestions cannot be applied.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.
Filling the whole command into 'sh -c' may hit length limit of single argument. For non-console subprocesses, use pipe to invoke sh instead.
Fixes #1261