DWARFS_IOLAYER_OPTS¶

The DWARFS_IOLAYER_OPTS environment variable can be used to configure certain aspects of the I/O layer used by all DwarFS tools. The value consists of a comma-separated list of key-value pairs (or just keys for boolean options). The following options are supported:

max_eager_map_size=value

The maximum size of a file that will be eagerly mapped into memory when opened. Larger files will be accessed using on-demand mappings. This is mostly relevant for 32-bit systems, where the address space is limited. value can be either unlimited, a size in bytes, or an integer value with a suffix of k, m, or g to indicate kibibytes, mebibytes, or gibibytes, respectively. The default is unlimited on 64-bit systems and 32 MiB on 32-bit systems.

open_mode=mmap|read

Chooses between memory-mapped I/O (mmap) and using "standard" read calls (pread) to access file data. The default is mmap, which is generally more efficient. If you have trouble with e.g. unreliable hardware or unstable network filesystems, this can easily cause a process accessing a memory-mapped file to crash with a bus error (SIGBUS). In such cases, you can try switching to read mode, which should prevent such crashes and deliver proper I/O error messages that can be useful for finding the root cause of the problem.