bug#70900: 30.0.50; tramp complains "File error: Cannot remove lock file for /ssh:..." on every save when remote-file-name-inhibit-locks is non-nil

[Michael Albinus via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Dmitry Gutov <dmitry@gutov.dev> writes:

Hi Dmitry,

> Still, it would be great if tramp could batch more checks to happen at
> once, rather than do them over multiple round-trips. Though that would
> mean having to maintain a separate "remote" version of
> 'basic-save-buffer', I guess.

Tramp tries to do this, but it is limited. It sees the remote side on
the perspective of a primitive file operation it has an implementation
for, see the list on (info "(elisp) Magic File Names")

And yes, 'basic-save-buffer' doesn't belong to this list.

Tramp tries to combine several actions in order to decrease the number
of roundtrips. And it uses caches. But all of this is mimited.

Tramp offers s special trace mode which shows you the external commands
it sends per primitive file operation. Call something like

--8<---------------cut here---------------start------------->8---
# emacs -Q --eval '(setq tramp-debug-command-messages t)' /ssh::
--8<---------------cut here---------------end--------------->8---

In the debug buffer, there are messages of level 4 (entering a primitive
file operation), level 5 (exiting the same operation), and level 6 (the
remote commands Tramp emits). Like

--8<---------------cut here---------------start------------->8---
12:11:26.513974 tramp-sh-handle-file-exists-p (4) # Running `(file-exists-p "/ssh:gandalf:/net/ford/albinus/Books.org")' ...
12:11:26.514344 tramp-send-command (6) # test -e /net/ford/albinus/Books.org 2>/dev/null; echo tramp_exit_status $?
12:11:26.530496 tramp-wait-for-regexp (6) #
tramp_exit_status 0
///fd26d4d0719c81d3c6e45f14adefee05#$
12:11:26.530742 tramp-sh-handle-file-exists-p (5) # Running `(file-exists-p "/ssh:gandalf:/net/ford/albinus/Books.org")' ... t
--8<---------------cut here---------------end--------------->8---

This is my tool to analyze. Several optimiztations have been performed
already, but there is still room for improvement, proposals/patches
welcome.

Best regards, Michael.