Don't put blob files on /tmp

[dcolascione]

blobchunk.c uses erofs_tmpfile to make a file in which to store blob data. erofs_tmpfile, unless configured otherwise, uses $TMPDIR or /tmp. Problem is $TMPDIR or /tmp can be a tmpfs, and mkfs.erofs can use a lot of temporary storage, filling up /tmp (by default sized for half of RAM) and causing various bits of mayhem throughout the system. You want to either use memfd_create to get the temporary FD or just stick your blobs in anonymous memory without going through a FD at all instead of mucking with /tmp.

[hsiangkao]

blobchunk.c will be changed in the near future, but it will not be changed for the upcoming erofs-utils 1.9.
If tmpfs is not enough, it's expected to either back /tmp with a real filesystem, or specify $TMPDIR to a real storage instead.