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The current code does not always assign proper udev flags to sub-LVs (e.g. mirror images and log LVs). This shows up especially during a splitmirror operation in which an image is split off from a mirror to form a new LV. A mirror with a disk log is actually composed of 4 different LVs: the 2 mirror images, the log, and the top-level LV that "glues" them all together. When a 2-way mirror is split into two linear LVs, two of those LVs must be removed. The segments of the image which is not split off to form the new LV are transferred to the top-level LV. This is done so that the original LV can maintain its major/minor, UUID, and name. The sub-lv from which the segments were transferred gets an error segment as a transitory process before it is eventually removed. (Note that if the error target was not put in place, a resume_lv would result in two LVs pointing to the same segment! If the machine crashes before the eventual removal of the sub-LV, the result would be a residual LV with the same mapping as the original (now linear) LV.) So, the two LVs that need to be removed are now the log device and the sub-LV with the error segment. If udev_flags are not properly set, a resume will cause the error LV to come up and be scanned by udev. This causes I/O errors. Additionally, when udev scans sub-LVs (or former sub-LVs), it can cause races when we are trying to remove those LVs. This is especially bad during failure conditions. When the mirror is suspended, the top-level along with its sub-LVs are suspended. The changes (now 2 linear devices and the yet-to-be-removed log and error LV) are committed. When the resume takes place on the original LV, there are no longer links to the other sub-lvs through the LVM metadata. The links are implicitly handled by querying the kernel for a list of dependencies. This is done in the '_add_dev' function (which is recursively called for each dependency found) - called through the following chain: _add_dev dm_tree_add_dev_with_udev_flags <*** DM / LVM divide ***> _add_dev_to_dtree _add_lv_to_dtree _create_partial_dtree _tree_action dev_manager_activate _lv_activate_lv _lv_resume lv_resume_if_active When udev flags are calculated by '_get_udev_flags', it is done by referencing the 'logical_volume' structure. Those flags are then passed down into 'dm_tree_add_dev_with_udev_flags', which in turn passes them to '_add_dev'. Unfortunately, when '_add_dev' is finding the dependencies, it has no way to calculate their proper udev_flags. This is because it is below the DM/LVM divide - it doesn't have access to the logical_volume structure. In fact, '_add_dev' simply reuses the udev_flags given for the initial device! This virtually guarentees the udev_flags are wrong for all the dependencies unless they are reset by some other mechanism. The current code provides no such mechanism. Even if '_add_new_lv_to_dtree' were called on the sub-devices - which it isn't - entries already in the tree are simply passed over, failing to reset any udev_flags. The solution must retain its implicit nature of discovering dependencies and be able to go back over the dependencies found to properly set the udev_flags. My solution simply calls a new function before leaving '_add_new_lv_to_dtree' that iterates over the dtree nodes to properly reset the udev_flags of any children. It is important that this function occur after the '_add_dev' has done its job of querying the kernel for a list of dependencies. It is this list of children that we use to look up their respective LVs and properly calculate the udev_flags. This solution has worked for single machine, cluster, and cluster w/ exclusive activation. |
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| .. | ||
| datastruct | ||
| ioctl | ||
| misc | ||
| mm | ||
| regex | ||
| .exported_symbols | ||
| libdevmapper.h | ||
| libdevmapper.pc.in | ||
| libdm-common.c | ||
| libdm-common.h | ||
| libdm-config.c | ||
| libdm-deptree.c | ||
| libdm-file.c | ||
| libdm-report.c | ||
| libdm-string.c | ||
| Makefile.in | ||