2 Commits

Author	SHA1	Message	Date
Brian Atkinson	b4e4cbeb20	Always validate checksums for Direct I/O reads ... This fixes an oversight in the Direct I/O PR. There is nothing that stops a process from manipulating the contents of a buffer for a Direct I/O read while the I/O is in flight. This can lead checksum verify failures. However, the disk contents are still correct, and this would lead to false reporting of checksum validation failures. To remedy this, all Direct I/O reads that have a checksum verification failure are treated as suspicious. In the event a checksum validation failure occurs for a Direct I/O read, then the I/O request will be reissued though the ARC. This allows for actual validation to happen and removes any possibility of the buffer being manipulated after the I/O has been issued. Just as with Direct I/O write checksum validation failures, Direct I/O read checksum validation failures are reported though zpool status -d in the DIO column. Also the zevent has been updated to have both: 1. dio_verify_wr -> Checksum verification failure for writes 2. dio_verify_rd -> Checksum verification failure for reads. This allows for determining what I/O operation was the culprit for the checksum verification failure. All DIO errors are reported only on the top-level VDEV. Even though FreeBSD can write protect pages (stable pages) it still has the same issue as Linux with Direct I/O reads. This commit updates the following: 1. Propogates checksum failures for reads all the way up to the top-level VDEV. 2. Reports errors through zpool status -d as DIO. 3. Has two zevents for checksum verify errors with Direct I/O. One for read and one for write. 4. Updates FreeBSD ABD code to also check for ABD_FLAG_FROM_PAGES and handle ABD buffer contents validation the same as Linux. 5. Updated manipulate_user_buffer.c to also manipulate a buffer while a Direct I/O read is taking place. 6. Adds a new ZTS test case dio_read_verify that stress tests the new code. 7. Updated man pages. 8. Added an IMPLY statement to zio_checksum_verify() to make sure that Direct I/O reads are not issued as speculative. 9. Removed self healing through mirror, raidz, and dRAID VDEVs for Direct I/O reads. This issue was first observed when installing a Windows 11 VM on a ZFS dataset with the dataset property direct set to always. The zpool devices would report checksum failures, but running a subsequent zpool scrub would not repair any data and report no errors. Reviewed-by: Tony Hutter <hutter2@llnl.gov> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Signed-off-by: Brian Atkinson <batkinson@lanl.gov> Closes #16598	2024-10-09 12:28:08 -07:00
Brian Atkinson	a10e552b99	Adding Direct IO Support ... Adding O_DIRECT support to ZFS to bypass the ARC for writes/reads. O_DIRECT support in ZFS will always ensure there is coherency between buffered and O_DIRECT IO requests. This ensures that all IO requests, whether buffered or direct, will see the same file contents at all times. Just as in other FS's , O_DIRECT does not imply O_SYNC. While data is written directly to VDEV disks, metadata will not be synced until the associated TXG is synced. For both O_DIRECT read and write request the offset and request sizes, at a minimum, must be PAGE_SIZE aligned. In the event they are not, then EINVAL is returned unless the direct property is set to always (see below). For O_DIRECT writes: The request also must be block aligned (recordsize) or the write request will take the normal (buffered) write path. In the event that request is block aligned and a cached copy of the buffer in the ARC, then it will be discarded from the ARC forcing all further reads to retrieve the data from disk. For O_DIRECT reads: The only alignment restrictions are PAGE_SIZE alignment. In the event that the requested data is in buffered (in the ARC) it will just be copied from the ARC into the user buffer. For both O_DIRECT writes and reads the O_DIRECT flag will be ignored in the event that file contents are mmap'ed. In this case, all requests that are at least PAGE_SIZE aligned will just fall back to the buffered paths. If the request however is not PAGE_SIZE aligned, EINVAL will be returned as always regardless if the file's contents are mmap'ed. Since O_DIRECT writes go through the normal ZIO pipeline, the following operations are supported just as with normal buffered writes: Checksum Compression Encryption Erasure Coding There is one caveat for the data integrity of O_DIRECT writes that is distinct for each of the OS's supported by ZFS. FreeBSD - FreeBSD is able to place user pages under write protection so any data in the user buffers and written directly down to the VDEV disks is guaranteed to not change. There is no concern with data integrity and O_DIRECT writes. Linux - Linux is not able to place anonymous user pages under write protection. Because of this, if the user decides to manipulate the page contents while the write operation is occurring, data integrity can not be guaranteed. However, there is a module parameter `zfs_vdev_direct_write_verify` that controls the if a O_DIRECT writes that can occur to a top-level VDEV before a checksum verify is run before the contents of the I/O buffer are committed to disk. In the event of a checksum verification failure the write will return EIO. The number of O_DIRECT write checksum verification errors can be observed by doing `zpool status -d`, which will list all verification errors that have occurred on a top-level VDEV. Along with `zpool status`, a ZED event will be issues as `dio_verify` when a checksum verification error occurs. ZVOLs and dedup is not currently supported with Direct I/O. A new dataset property `direct` has been added with the following 3 allowable values: disabled - Accepts O_DIRECT flag, but silently ignores it and treats the request as a buffered IO request. standard - Follows the alignment restrictions outlined above for write/read IO requests when the O_DIRECT flag is used. always - Treats every write/read IO request as though it passed O_DIRECT and will do O_DIRECT if the alignment restrictions are met otherwise will redirect through the ARC. This property will not allow a request to fail. There is also a module parameter zfs_dio_enabled that can be used to force all reads and writes through the ARC. By setting this module parameter to 0, it mimics as if the direct dataset property is set to disabled. Reviewed-by: Brian Behlendorf <behlendorf@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Reviewed-by: Tony Hutter <hutter2@llnl.gov> Signed-off-by: Brian Atkinson <batkinson@lanl.gov> Co-authored-by: Mark Maybee <mark.maybee@delphix.com> Co-authored-by: Matt Macy <mmacy@FreeBSD.org> Co-authored-by: Brian Behlendorf <behlendorf@llnl.gov> Closes #10018	2024-09-14 13:47:59 -07:00