On Thu, Apr 26, 2007 at 11:20:56PM +0530, Amit K. Arora wrote: > Based on the discussion, this new patchset uses following as the > interface for fallocate() system call: > > asmlinkage long sys_fallocate(int fd, int mode, loff_t offset, loff_t len) Ok, so now for the hard questions - what are the semantics of FA_ALLOCATE and FA_DEALLOCATE? For FA_ALLOCATE, it's supposed to change the file size if we allocate past EOF, right? What's the return value supposed to be? Zero for success, error otherwise? Does this update a/m/ctime at all? How persistent is this preallocation? Should it be there "forever" or for the lifetime of the currently open fd that it was preallocated on? For FA_DEALLOCATE, does it change the filesize at all? Or does it just punch a hole in the file? If it does change file size, what happens when you punch out preallocation beyond EOF? What's the return value supposed to be? > Currently we have two modes FA_ALLOCATE and FA_DEALLOCATE, for > preallocation and deallocation of preallocated blocks respectively. More > modes can be added, when required. FWIW, we definitely need a FA_PREALLOCATE mode (FA_ALLOCATE but does not change file size) so we can preallocate beyond EOF for apps which use O_APPEND (i.e. changing file size would cause problems for them). > ToDos: > ===== > 1> Implementation on other architectures (other than i386, x86_64, > ppc64 and s390(x)) I'll have ia64 soon. > 2> A generic file system operation to handle fallocate > (generic_fallocate), for filesystems that do _not_ have the fallocate > inode operation implemented. > 3> Changes to glibc, > a) to support fallocate() system call > b) so that posix_fallocate() and posix_fallocate64() call > fallocate() system call > 4> Changes to XFS to implement the fallocate inode operation And that's what I'm doing now, hence all the questions ;) BTW, do you have a test program for this, or will I need to write one myself? Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
