dirfs.OpenFile can return EEXIST even if that is not defined FS.OpenFile in the interface documentation

[karelbilek]

In the interface FS.OpenFile, you have defined a set of errors that OpenFile can return.

https://github.com/tetratelabs/wazero/blob/ba569623fcb7b32bb8fc64dadc842672befd6819/experimental/sys/fs.go#L34...L39

However, if you follow what DirFS can return, there are more possible errors

https://github.com/tetratelabs/wazero/blob/ba569623fcb7b32bb8fc64dadc842672befd6819/experimental/sys/error.go#L10...L30

For example, if one opens file with O_CREAT and O_EXCL, but the file exists already, POSIX OS will return EEXIST.

I am implementing a custom FS, and I am not sure what to follow; there is a mismatch between the docs say and what the DirFS actually does.

[karelbilek]

When I follow it to the "other side", I see this

https://github.com/tetratelabs/wazero/blob/ba569623fcb7b32bb8fc64dadc842672befd6819/imports/wasi_snapshot_preview1/fs.go#L1534...L1540

EEXIST is there.

I don't see any list of allowed errnos here

https://github.com/WebAssembly/WASI/blob/main/legacy/preview1/docs.md#path_open

or here

https://wasix.org/docs/api-reference/wasi/path_open

so... I guess it can return EEXIST?

[evacchi]

indeed, there are case where we return EEXIST https://github.com/tetratelabs/wazero/blame/main/experimental/sys/fs.go when we do it is usually because there is a test that requires it; e.g. in wasi-testsuite or other test suites. I will double check the docs to make sure they are up to date.

[karelbilek]

As written in #2104 I figured out there are other errors that are not in the docs.

I wanted to make a PR with all the possible errnos, but then I realized, all I am doing is rewriting https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html (the ERRORS part) to godoc format.

At which point I realized I might be even breaking copyright, as POSIX docs are copyrighted.

Wouldn't it be better to just link to the posix errors and say "here, there is a list"? It's documented better than will be here... the list on POSIX docs is very exhaustive.

Or, just rewrite the docs from "The below are expected otherwise..." to "Some possible errors: ..."?

[karelbilek]

Hm, but only SOME of those actually matter here. Hm. I guess I get back to rewriting. (But in my own words.)

edit: hm, no, I will not rewrite this, I can just copy-paste that

A component of the path prefix names an existing file that is neither a directory nor a symbolic link to a directory; or O_CREAT and O_EXCL are not specified, the path argument contains at least one non- character and ends with one or more trailing characters, and the last pathname component names an existing file that is neither a directory nor a symbolic link to a directory; or O_DIRECTORY was specified and the path argument resolves to a non-directory file.