Allow /tmp and /var to be on different partitions - invalid cross-device link

[YBonline]

My system is setup with /var on its own partition, along with /tmp being a tmpfs

Whenever trying to use uhppoted-httpd when it tries to write to the files, it always gives a rename : invalid cross-device link error

My understand is you need to use move instead of rename to account for them being separate partitions.

[uhppoted]

Huh! In theory Go Rename is supposed to do a move:

Rename renames (moves) oldpath to newpath. If newpath already exists and is not a directory, Rename replaces it. OS-specific restrictions may apply when oldpath and newpath are in different directories. Even within the same directory, on non-Unix platforms Rename is not an atomic operation.

I wonder if they tested it on a tmpfs .. ok, let me look into it.

[YBonline]

https://stackoverflow.com/questions/42392600/oserror-errno-18-invalid-cross-device-link

os.rename only works if source and destination are on the same file system. You should use shutil.move instead.

At least according to my googling

[uhppoted]

Seems to be an open issue in Go: #41487 os: if rename system call fails, try ioctl(FICLONE).

Hmm, I use os.Rename everywhere ... ok, am going to have to figure out a nice way to do it.

[uhppoted]

Hi,

Well, that was minor can of worms :-) .. however, FWIW, there's a provisional fix for this issue in the main branch which:

1. First attempts to do a rename
2. If the rename fails then attempts to do a file copy and delete

The actual change turned out to be fairly small and relatively low impact - I've tested it briefly and it behaves as expected.

If you would like to try it out you'll have to clone the repo and build it locally. Which is reasonably straightforward - the instructions are in the README (Building from source) but if it's problem let me know and I can put up a nightly build on github.

Note: the current implementation can potentially leave a temporary file in place if the machine crashes while copying the file. Hopefully this should be rare enough not to be an immediate problem while I work on cleaning up temporary files on startup.

[uhppoted]

Ok, uhppoted-httpd should be good to go.

NTS: also update:

• uhppoted-app-db
• uhppoted-app-sheets
• uhppoted-app-wild-apricot
• uhppoted-codegen
• uhppoted-lib:eventlog
• uhppoted-lib:listen
• uhppoted-lib:kvs

[uhppoted]

And that's a wrap .. will leave this open for a couple of days in case something weird turns up.

[uhppoted]

Closing this - seems to be ok so far. Feel free to reopen if you run into anything.