Bug 251417

Summary:	editing files deletes them, destroying hardlinks
Product:	[Frameworks and Libraries] kio-extras	Reporter:	H.H. <cyberbeat>
Component:	SFTP	Assignee:	Andreas Schneider <asn>
Status:	RESOLVED UPSTREAM
Severity:	major	CC:	sitter
Priority:	NOR
Version First Reported In:	18.04.3
Target Milestone:	---
Platform:	openSUSE
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description H.H. 2010-09-16 09:36:15 UTC

Version:           0.1 (using KDE 4.5.1) 
OS:                Linux

This is really a severe bug, because it has bad side-effects on hardlinks:

1) open a file with multiple hardlinks directly via kio_sftp in kwrite
2) modify the file
3) save file

--> the original hardlink is deleted and a new file is created

The kio_fish-protocol behaves like expected (not deleting the hardlink)

Reproducible: Always




OS: Linux (x86_64) release 2.6.27.25-0.1-default
Compiler: gcc

Comment 1 Andreas Schneider 2010-09-16 11:15:49 UTC

Thank you for taking the time to report this bug and helping to make KDE better.

The kio_sftp slaves tries to do an atomic copy to prevent data loss.

If you copy a file to the server, it creates a temporary file. All data is written into this file and if it was successful the original file gets overwritten. This means that the hardlink gets overwritten in your case.

As the sftp protocol has never been finished there is no way to determine if a file is a hardlink or not. Only symlinks are supported and only with a trick on openssh.

Comment 2 H.H. 2010-09-16 19:29:54 UTC

how does fish do that? I have seen multiple google-results for "sftp hardlinks", there seem to exist some patches, but I don't know if and where they are integrated.

Comment 3 Andreas Schneider 2010-09-17 01:14:21 UTC

The sftp rename implementation is not a POSIX rename. Maybe a POSIX rename does it correctly.

OpenSSH has an sftp extension for a posix-rename. I could implement that and enable it for OpenSSH servers then.

Comment 4 H.H. 2018-07-20 21:47:20 UTC

That would be great. Here is the bug-report in openssh, and proof that openssh-5.7 supports hardlinks:

https://bugzilla.mindrot.org/show_bug.cgi?id=1555

Comment 8:
hard link patch is submitted and will be released in OpenSSH 5.7

Comment 5 Andreas Schneider 2018-09-03 05:59:27 UTC

I've opened https://bugs.libssh.org/T98

Comment 6 Harald Sitter 2020-03-04 15:06:48 UTC

Closing as this needs dealing with in libssh upstream.