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dm-error is used in several test cases in the xfstests test suite to check the handling of IO errors in file systems. However, with several file systems getting native support for zoned block devices (e.g. btrfs and f2fs), dm-error's lack of zoned block device support creates problems as the file system attempts executing zone commands (e.g. a zone append operation) against a dm-error non-zoned block device, which causes various issues in the block layer (e.g. WARN_ON triggers). This commit adds supports for zoned block devices to dm-error, allowing a DM device table containing an error target to be exposed as a zoned block device (if all targets have a compatible zoned model support and mapping). This is done as follows: 1) Allow passing 2 arguments to an error target, similar to dm-linear: a backing device and a start sector. These arguments are optional and dm-error retains its characteristics if the arguments are not specified. 2) Implement the iterate_devices method so that dm-core can normally check the zone support and restrictions (e.g. zone alignment of the targets). When the backing device arguments are not specified, the iterate_devices method never calls the fn() argument. When no backing device is specified, as before, we assume that the DM device is not zoned. When the backing device arguments are specified, the zoned model of the DM device will depend on the backing device type: - If the backing device is zoned and its model and mapping is compatible with other targets of the device, the resulting device will be zoned, with the dm-error mapped portion always returning errors (similar to the default non-zoned case). - If the backing device is not zoned, then the DM device will not be either. This zone support for dm-error requires the definition of a functional report_zones operation so that dm_revalidate_zones() can operate correctly and resources for emulating zone append operations initialized. This is necessary for cases where dm-error is used to partially map a device and have an overall correct handling of zone append. This means that dm-error does not fail report zones operations. Two changes that are not obvious are included to avoid issues: 1) dm_table_supports_zoned_model() is changed to directly check if the backing device of a wildcard target (= dm-error target) is zoned. Otherwise, we wouldn't be able to catch the invalid setup of dm-error without a backing device (non zoned case) being combined with zoned targets. 2) dm_table_supports_dax() is modified to return false if the wildcard target is found. Otherwise, when dm-error is set without a backing device, we end up with a NULL pointer dereference in set_dax_synchronous (dax_dev is NULL). This is consistent with the current behavior because dm_table_supports_dax() always returned false for targets that do not define the iterate_devices method. Signed-off-by: Damien Le Moal <dlemoal@kernel.org> Tested-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Mike Snitzer <snitzer@kernel.org> |
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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.