https://bugzilla.mindrot.org/show_bug.cgi?id=3979
Bug ID: 3979
Summary: Use reflink for fast cross filesystem copy and rename
Product: Portable OpenSSH
Version: 10.4p1
Hardware: amd64
OS: Solaris
Status: NEW
Severity: enhancement
Priority: P5
Component: sftp-server
Assignee: [email protected]
Reporter: [email protected]
The reflink() call provides a very fast mechanism to copy files.
Unlike link() it isn't a pointer to the same file but a new file that
the underlying filesystem arranges to be a copy (but without it
manually reading/writing all the blocks). For ZFS on Solaris you can
do cross file system copy within the ZFS storage pool.
The sftp-server copy-data can be implemented using reflink() with a
fallback to the existing read/write loop.
For sftp-server rename there is an existing method that uses
link/unlink instead of rename. Both the link/unlink method and rename
don't work across filesystem boundaries but a reflink/unlink will.
For the rename case while we could introduce a new protocol extension,
it seems simpler make this an implementation detail. Note that because
of the [email protected] extension the OpenSSH sftp(1) client
would need to do 'rename -l old new' otherwise the extension is used
instead.
Attached is a patch that shows a proof of concept of how this could be
done. It isn't intended to be integration ready because there would
need to be appropriate checks added for the system having reflink. It
has so far only been tested on Solaris 11.4 with OpenSSH 10.3 with an
SFTP client from an older OpenSSH release on Linux.
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