fs.Dir: Give the option to stat a symbolic link

[samy-00007]

This pull request adds Dir.statLink (with Z and W variants) to stat symlink.
It also improves the windows version of Dir.statFile.

[alexrp]

Note that this will need Linux-specific statx()-based code once #20389 is merged.

[alexrp]

Note that this will need Linux-specific statx()-based code once #20389 is merged.

Just dropping in again to say that it has been merged.

[samy-00007]

I will make the necessary changes.

[samy-00007]

It should be good.

[samy-00007]

From what i am seeing, the test fails with wasm because in stage1/wasi.c, DirEntry_lookup which is used to stat the file ignores the flags, and so follows the symlink. Should i skip the test for wasi ? (Unless this is not the where the wasm functions are defined. I don't know enough about that)

[squeek502]

Unless this is not the where the wasm functions are defined. I don't know enough about that

That's not the relevant code for the test failure (that's only used for bootstrapping a Zig compiler).

My guess is that it's wasi-libc which is ignoring the AT.SYMLINK_NOFOLLOW flag of fstat called from here, but will need to confirm (see #20747 for a similar wasi-libc bug). My second guess is that this test failure will only be present when linking wasi-libc, but also need to confirm that.

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EDIT: Confirmed both guesses:

strace of the Dir.readLink function when linking wasi-libc (lack of O_NOFOLLOW in the openat2 flags):

openat2(13, "symlink", {flags=O_RDONLY|O_CLOEXEC|O_PATH, resolve=RESOLVE_NO_MAGICLINKS|RESOLVE_BENEATH}, 24) = 11
statx(11, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=17, ...}) = 0
close(11)                               = 0

and without (inclusion of O_NOFOLLOW in the openat2 flags):

openat2(13, "symlink", {flags=O_RDONLY|O_NOFOLLOW|O_CLOEXEC|O_PATH, resolve=RESOLVE_NO_MAGICLINKS|RESOLVE_BENEATH}, 24) = 11
statx(11, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFLNK|0777, stx_size=9, ...}) = 0
close(11)                               = 0

This is very likely to be either a wasmtime or a wasi-libc bug. Will try to put together a reproduction with wasi-sdk and report it downstream.

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EDIT#2: Unable to find a reproduction, filed a follow-up issue: #20890

[samy-00007]

Is it possible to redo the CI tests ? They did not fail because of my code

[squeek502]

Rebase the branch onto the latest master branch and it should get fixed.

[samy-00007]

Is it good ?

[squeek502]

Looks good to me.

One possible variation on this would be to make statFile take an options struct parameter with a follow_symlinks field (instead of having separate pub statLink functions). Unsure which would be better, will leave that up to the core team member(s) that review this.

[alexrp]

One possible variation on this would be to make statFile take an options struct parameter with a follow_symlinks field (instead of having separate pub statLink functions). Unsure which would be better, will leave that up to the core team member(s) that review this.

I think I lean towards preferring this FWIW. What other options do we imagine might come up in the future?