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Zlibc

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Reaction to a readonly request

The reaction to a readonly request may be one of the following:

show-pipe
The uncompressed data file is sent to the user program using a pipe. This consumes very few resources, and it allows the decompression to run in paralell with the user process, but it has the disadvantage that the user program cannot use lseek. To warn the user program of this, the data file is shown as a named pipe (FIFO) when it is stat'ed.

use-tmp-file
This is the default setting. The data is uncompressed and put into a temporary file. The user programs then reads its data from the temporary file. This has the advantage that the user program may lseek, and the disadvantage that more disk space is consumed, while the programming is accessing the file.

hide-pipe
The data is sent through a pipe, but the file is shown as a regular file ("hidden") to the user program when it stats it. This might be needed for programs which are picky about a file type, but who actually don't need lseek.

leave-compressed
The virtual (uncompressed) file is shown as non-existent to stat, and readdir shows the physical (compressed) file. For certain programs, this is enough to disable zlibc on a file per file basis. This is useful, for example, to make emacs use its own compression support (crypt.el) instead of zlibc. Crypt.el is able to compress files when writing them back, whereas zlibc isn't able to do so. The leave-compressed doesn't work correctly with the directory and subdirectory criteria. Use the filesystem criterion instead.

dir-leave-compressed
The virtual (uncompressed) file is shown to stat, but readdir shows the physical (compressed) file. This is useful to tell zlibc that we prefer working on the physical file, but without making access to the virtual file impossible. The dir-leave-compressed doesn't work with the dir and subdir criteria. Use the filesystem criterion instead.


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