Block devices in the Linux kernel have a "minimum I/O request" size. The
minimum size is usually acquired by the block driver and can change
from device to device. When stacking devices (such as with
device-mapper), the kernel goes through great lengths to make sure this
alignment is respected for optimal I/O. In device-mapper's case,
misalignment can lead to kernel warnings and performance issues.
While this is unlikely to matter with a few targets, it could become
problematic on a large number of targets, and so we would prefer to
align all partition extents to the minimum I/O size.
We now support two new properties in the partition table geometry: an
"alignment", which is the minimum I/O size, and an "alignment offset",
which is an offset that when applied to sector 0, causes the sector to
be properly aligned within its parent device (for example, if a
physical partition is misaligned). All partition extents now begin on a
sector that respects this alignment.
One major caveat is that it is difficult for the initial partition table
to have the correct alignment without build system and/or flash tool
support. To accomodate this, all alignment is optional, and the lpmake
tool will support a default alignment of 1MiB as a failsafe.
Bug: 79173901
Test: liblp_test gtest
Change-Id: I5bc41b90aa085f4f30393951af0d2b37c4ac2a72
This library has methods to build, read, and modify logical partition tables
based on device-mapper targets. Targets currently supported are
dm-linear and dm-zero.
Note: this is a revert of a revert, with changes to fix Mac build
bustage.
Bug: 79173901
Test: N/A
Change-Id: If89a788d1919ce8ddc6eedaecc9687a92f111dfa
This library has methods to build, read, and modify logical partition tables
based on device-mapper targets. Targets currently supported are
dm-linear and dm-zero.
Bug: 79173901
Test: N/A
Change-Id: I194c6832cb53f781c396016d961386d3ca833f87
David Anderson