9f1833cadd
This closes a significant hole (and last known hole) in our ability to verify metadata. Previously, since btree nodes are log structured, we couldn't detect lost btree writes that weren't the first write to a given node. Additionally, this seems to have lead to some significant metadata corruption on multi device filesystems with metadata replication: since a write may have made it to one device and not another, if we read that btree node back from the replica that did have that write and started appending after that point, the other replica would have a gap in the bset entries and reading from that replica wouldn't find the rest of the bsets. But, since updates to interior btree nodes are now journalled, we can close this hole by updating pointers to btree nodes after every write with the currently written number of sectors, without negatively affecting performance. This means we will always detect lost or corrupt metadata - it also means that our btree is now a curious hybrid of COW and non COW btrees, with all the benefits of both (excluding complexity). Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.