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File incorrectly zeroed when receiving incremental stream that toggle…
…s -L Background: By increasing the recordsize property above the default of 128KB, a filesystem may have "large" blocks. By default, a send stream of such a filesystem does not contain large WRITE records, instead it decreases objects' block sizes to 128KB and splits the large blocks into 128KB blocks, allowing the large-block filesystem to be received by a system that does not support the `large_blocks` feature. A send stream generated by `zfs send -L` (or `--large-block`) preserves the large block size on the receiving system, by using large WRITE records. When receiving an incremental send stream for a filesystem with large blocks, if the send stream's -L flag was toggled, a bug is encountered in which the file's contents are incorrectly zeroed out. The contents of any blocks that were not modified by this send stream will be lost. "Toggled" means that the previous send used `-L`, but this incremental does not use `-L` (-L to no-L); or that the previous send did not use `-L`, but this incremental does use `-L` (no-L to -L). Changes: This commit addresses the problem with several changes to the semantics of zfs send/receive: 1. "-L to no-L" incrementals are rejected. If the previous send used `-L`, but this incremental does not use `-L`, the `zfs receive` will fail with this error message: incremental send stream requires -L (--large-block), to match previous receive. 2. "no-L to -L" incrementals are handled correctly, preserving the smaller (128KB) block size of any already-received files that used large blocks on the sending system but were split by `zfs send` without the `-L` flag. 3. A new send stream format flag is added, `SWITCH_TO_LARGE_BLOCKS`. This feature indicates that we can correctly handle "no-L to -L" incrementals. This flag is currently not set on any send streams. In the future, we intend for incremental send streams of snapshots that have large blocks to use `-L` by default, and these streams will also have the `SWITCH_TO_LARGE_BLOCKS` feature set. This ensures that streams from the default use of `zfs send` won't encounter the bug mentioned above, because they can't be received by software with the bug. Implementation notes: To facilitate accessing the ZPL's generation number, `zfs_space_delta_cb()` has been renamed to `zpl_get_file_info()` and restructured to fill in a struct with ZPL-specific info including owner and generation. In the "no-L to -L" case, if this is a compressed send stream (from `zfs send -cL`), large WRITE records that are being written to small (128KB) blocksize files need to be decompressed so that they can be written split up into multiple blocks. The zio pipeline will recompress each smaller block individually. A new test case, `send-L_toggle`, is added, which tests the "no-L to -L" case and verifies that we get an error for the "-L to no-L" case. Reviewed-by: Paul Dagnelie <pcd@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Matthew Ahrens <mahrens@delphix.com> Closes #6224 Closes #10383
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