Messages in this thread | | | Date | Fri, 1 Aug 2003 23:23:58 +0200 | From | Matthias Andree <> | Subject | File system synchronous completion poll. |
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Hi,
it's time again to poll for file system semantics with respect to synchronous completion, for MTA use.
Define: directory operations := link, rename, mkdir (symlink, rmdir, unlink)
Assume the drive's write cache is off (if your file system is safe with write cache on, because it queues ordered tags on SCSI, please state so):
For each of XFS, JFS, ext3fs, ext2fs, reiserfs-3.6, reiserfs-4, for both of 2.4.21 and 2.6.0-testX, please state (rationale below):
1. Is mount -o sync implemented? If not, does mount -o sync fail? If yes, does mount -o sync mean a) "all operations synchronous" or b) "directory operations" synchronous?
2. Is mount -o dirsync implemented?
3. Is chattr +S implemented, and inherited by freshly-created subdirectories?
4. Is chattr +D implemented, and inherited by freshly-created subdirectories?
5. Does fd=open("a", ...); rename("a", "b"); fsync(fd); close(fd); guarantee that "b" is on disk after fsync() has returned?
6. Which code fragment makes sure a directory is on disk? a. mkdir("parent/sub"); fd=open("parent"); fsync(fd); b. mkdir("parent/sub"); fd=open("parent/sub"); fsync(fd); This question may not be relevant if the system supports -o sync or -o dirsync.
7. Is rename("a", "b") truly atomic or can it cause a file to either end up in lost+found or be there as "a" and "b" in a crash?
The results should be recorded (with date of finding) in man mount(8).
I am aware that XFS, reiserfs and ext3fs as of Linux 2.4 commit all pending transactions within a file system when an fsync() is requested, however, this isn't always sufficient (particularly in the mkdir case, what do you open to fsync it?).
The rationale is to find out how much Linux file systems differ from BSD UFS + softupdates code, and how well which file system suits the opposite of the common tuning (data base): mail transfer agent. Their authors are still reluctant to add explicit fd=open("directory"); fsync(fd) code and assume traditional BSD "noasync" (= dirsync) semantics.
-- Matthias Andree - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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