Comment by macdice
7 years ago
What about this: you write() some data, and then Linux throws it away because of a writeback error, and later you read() it, and Linux gives you an older version from before your write (because this error condition has somehow been fixed and now it reads that block back into the page cache). I'm pretty sure that violates POSIX, which says:
"The read() function reads data previously written to a file."
I don't think that's the behavior, though. The blocks don't get flushed, they're still in cache and get read back. Probably. Again, the system broke. You've got no guarantees about anything. Fixing an API isn't going to change that.
API guarantees are still important even when a peripheral breaks. It's the difference between knowing how and where performance is degraded and what to work around, versus utter chaos.
Totally agree. Speaking as a database hacker, just tell me it broke. I will deal with the rest.
2 replies →
When a write-back error happens, Linux marks the block clean so it can be replaced by another block at any time. Additionally, some Linux filesystems (I don't recall which right now) proactively throw it away immediately.