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Under some circumstances, an incremental send operation can issue wrong
paths for unlink commands related to files that have multiple hard links
and some (or all) of those links were renamed between the parent and send
snapshots. Consider the following example:
Parent snapshot
. (ino 256)
|---- a/ (ino 257)
| |---- b/ (ino 259)
| | |---- c/ (ino 260)
| | |---- f2 (ino 261)
| |
| |---- f2l1 (ino 261)
|
|---- d/ (ino 262)
|---- f1l1_2 (ino 258)
|---- f2l2 (ino 261)
|---- f1_2 (ino 258)
Send snapshot
. (ino 256)
|---- a/ (ino 257)
| |---- f2l1/ (ino 263)
| |---- b2/ (ino 259)
| |---- c/ (ino 260)
| | |---- d3 (ino 262)
| | |---- f1l1_2 (ino 258)
| | |---- f2l2_2 (ino 261)
| | |---- f1_2 (ino 258)
| |
| |---- f2 (ino 261)
| |---- f1l2 (ino 258)
|
|---- d (ino 261)
When computing the incremental send stream the following steps happen:
1) When processing inode 261, a rename operation is issued that renames
inode 262, which currently as a path of "d", to an orphan name of
"o262-7-0". This is done because in the send snapshot, inode 261 has
of its hard links with a path of "d" as well.
2) Two link operations are issued that create the new hard links for
inode 261, whose names are "d" and "f2l2_2", at paths "/" and
"o262-7-0/" respectively.
3) Still while processing inode 261, unlink operations are issued to
remove the old hard links of inode 261, with names "f2l1" and "f2l2",
at paths "a/" and "d/". However path "d/" does not correspond anymore
to the directory inode 262 but corresponds instead to a hard link of
inode 261 (link command issued in the previous step). This makes the
receiver fail with a ENOTDIR error when attempting the unlink
operation.
The problem happens because before sending the unlink operation, we failed
to detect that inode 262 was one of ancestors for inode 261 in the parent
snapshot, and therefore we didn't recompute the path for inode 262 before
issuing the unlink operation for the link named "f2l2" of inode 262. The
detection failed because the function "is_ancestor()" only follows the
first hard link it finds for an inode instead of all of its hard links
(as it was originally created for being used with directories only, for
which only one hard link exists). So fix this by making "is_ancestor()"
follow all hard links of the input inode.
A test case for fstests follows soon.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.