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Support is divided into two main areas: - reading VPD pages and setting sdev request_queue limits - support WRITE ATOMIC (16) command and tracing The relevant block limits VPD page need to be read to allow the block layer request_queue atomic write limits to be set. These VPD page limits are described in sbc4r22 section 6.6.4 - Block limits VPD page. There are five limits of interest: - MAXIMUM ATOMIC TRANSFER LENGTH - ATOMIC ALIGNMENT - ATOMIC TRANSFER LENGTH GRANULARITY - MAXIMUM ATOMIC TRANSFER LENGTH WITH BOUNDARY - MAXIMUM ATOMIC BOUNDARY SIZE MAXIMUM ATOMIC TRANSFER LENGTH is the maximum length for a WRITE ATOMIC (16) command. It will not be greater than the device MAXIMUM TRANSFER LENGTH. ATOMIC ALIGNMENT and ATOMIC TRANSFER LENGTH GRANULARITY are the minimum alignment and length values for an atomic write in terms of logical blocks. Unlike NVMe, SCSI does not specify an LBA space boundary, but does specify a per-IO boundary granularity. The maximum boundary size is specified in MAXIMUM ATOMIC BOUNDARY SIZE. When used, this boundary value is set in the WRITE ATOMIC (16) ATOMIC BOUNDARY field - layout for the WRITE_ATOMIC_16 command can be found in sbc4r22 section 5.48. This boundary value is the granularity size at which the device may atomically write the data. A value of zero in WRITE ATOMIC (16) ATOMIC BOUNDARY field means that all data must be atomically written together. MAXIMUM ATOMIC TRANSFER LENGTH WITH BOUNDARY is the maximum atomic write length if a non-zero boundary value is set. For atomic write support, the WRITE ATOMIC (16) boundary is not of much interest, as the block layer expects each request submitted to be executed atomically. However, the SCSI spec does leave itself open to a quirky scenario where MAXIMUM ATOMIC TRANSFER LENGTH is zero, yet MAXIMUM ATOMIC TRANSFER LENGTH WITH BOUNDARY and MAXIMUM ATOMIC BOUNDARY SIZE are both non-zero. This case will be supported. To set the block layer request_queue atomic write capabilities, sanitize the VPD page limits and set limits as follows: - atomic_write_unit_min is derived from granularity and alignment values. If no granularity value is not set, use physical block size - atomic_write_unit_max is derived from MAXIMUM ATOMIC TRANSFER LENGTH. In the scenario where MAXIMUM ATOMIC TRANSFER LENGTH is zero and boundary limits are non-zero, use MAXIMUM ATOMIC BOUNDARY SIZE for atomic_write_unit_max. New flag scsi_disk.use_atomic_write_boundary is set for this scenario. - atomic_write_boundary_bytes is set to zero always SCSI also supports a WRITE ATOMIC (32) command, which is for type 2 protection enabled. This is not going to be supported now, so check for T10_PI_TYPE2_PROTECTION when setting any request_queue limits. To handle an atomic write request, add support for WRITE ATOMIC (16) command in handler sd_setup_atomic_cmnd(). Flag use_atomic_write_boundary is checked here for encoding ATOMIC BOUNDARY field. Trace info is also added for WRITE_ATOMIC_16 command. Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> Signed-off-by: John Garry <john.g.garry@oracle.com> Acked-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Link: https://lore.kernel.org/r/20240620125359.2684798-9-john.g.garry@oracle.com Signed-off-by: Jens Axboe <axboe@kernel.dk> |
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| kernel | ||
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| COPYING | ||
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| README | ||
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 reStructuredText 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.