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    SubjectRe: [PATCH 0/5] fallocate system call
    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

    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?


    Dave Chinner
    Principal Engineer
    SGI Australian Software Group
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