On Mon, 6 Oct 2025 at 12:57, Alejandro Colomar [off-list ref] wrote:

Hi Luca,

On Mon, Oct 06, 2025 at 12:46:41PM +0100, Luca Boccassi wrote:

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 .TP
+.B EINVAL
+The source mount is already mounted somewhere else. Clone it via

[...]

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+.BR open_tree (2)
+with
+.B \%OPEN_TREE_CLONE
+and use that as the source instead (since Linux 6.15).

The parenthetical in that position makes it unclear if you're saying
that one should use open_tree(2) with OPEN_TREE_CLONE since Linux 6.15,
or if you're saying that this error can happen since that version.
Would you mind clarifying?  I think if you mean that the error can
happen since Linux 6.15, we could make it part of the paragraph tag, as
in unshare(2).

I meant the former, the error is always there, but OPEN_TREE_CLONE can
be used since 6.15 to avoid it. Sent v2 with this and the other fix,
thanks for the prompt review.

Hmmm, I see.  Why not use open_tree(2) and OPEN_TREE_CLONE before 6.15?
The syscall and flag existed, AFAICS.  I think we should clarify --at
least in the commit message--, why that version is important.

It was just not supported at all, so it would still fail with EINVAL
before 6.15 even with the clone.

Thanks!  What's the exact commit (or set of commits) that changed this?
That would be useful for the commit message.

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Would you like me to send a v3 or would you prefer to amend the commit
message yourself?

I can amend myself.

Sorry, I am not a kernel dev so I do not know where it was introduced
exactly, and quickly skimming the commits list doesn't immediately
reveal anything. I only know that by testing it, it works on 6.15 and
fails earlier.