|Summary:||Please add direct support for the Linux system call fallocate(2)|
|Product:||glibc||Reporter:||Theodore Tso <tytso>|
|Component:||libc||Assignee:||Ulrich Drepper <drepper.fsp>|
Description Theodore Tso 2008-12-09 06:30:49 UTC
Currently, the Linux fallocate system call is only exposed via glibc's posix_fallocate() interface. Unfortunately, this means it is not possible for the user to pass in the FALLOC_FL_KEEP_SIZE flag. This flag reserves blocks for use by the inode, but without changing the size of the file as reported by i_size. This can be useful in some circumstances. For example, a program that rotates logfiles might want to use fallocate() with FALLOC_FL_KEEP_SIZE to reserve space for the new /var/log/messages file, without changing the reported i_size of the file. This allows the new /var/log/messages file to be contiguous, while still allowing tail -f to work, and log analyzers to read from the file without getting a large number of trailing zero's --- which would be the case if posix_fallocate() (which does not use FALLOC_FL_KEEP_SIZE flag, as required by POSIX specification) were used to preallocate the file. For this reason, we need a glibc-mediated interface that exposes the Linux fallocate system call's flags field. Without this, I will have to recommend that programs that wish to use this functionality (which is implemented in ext4 and xfs) will have to call the system call directly, which would be hard to make portable across different Linux architectures. Many thanks!
Comment 1 Ulrich Drepper 2009-03-02 16:17:47 UTC
I've added fallocate and fallocate64 functions.