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The move_blocks ioctl intends to only move extents whose bytes fall inside i_size. This is easy except for a final extent that straddles an i_size that isn't aligned to 4K data blocks. The code that either checked for an extent being entirely past i_size or for limiting the number of blocks to move by i_size clumsily compared i_size offsets in bytes with extent counts in 4KB blocks. In just the right circumstances, probably with the help of a byte length to move that is much larger than i_size, the length calculation could result in trying to move 0 blocks. Once this hit the loop would keep finding that extent and calculating 0 blocks to move and would be stuck. We fix this by clamping the count of blocks in extents to move in terms of byte offsets at the start of the loop. This gets rid of the extra size checks and byte offset use in the loop. We also add a sanity check to make sure that we can't get stuck if, say, corruption resulted in an otherwise impossible zero length extent. Signed-off-by: Zach Brown <zab@versity.com>
Introduction
scoutfs is a clustered in-kernel Linux filesystem designed to support large archival systems. It features additional interfaces and metadata so that archive agents can perform their maintenance workflows without walking all the files in the namespace. Its cluster support lets deployments add nodes to satisfy archival tier bandwidth targets.
The design goal is to reach file populations in the trillions, with the archival bandwidth to match, while remaining operational and responsive.
Highlights of the design and implementation include:
- Fully consistent POSIX semantics between nodes
- Atomic transactions to maintain consistent persistent structures
- Integrated archival metadata replaces syncing to external databases
- Dynamic seperation of resources lets nodes write in parallel
- 64bit throughout; no limits on file or directory sizes or counts
- Open GPLv2 implementation
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