io_uring_prep_fallocate - Linux

Overview

io_uring_prep_fallocate prepares an asynchronous file allocation operation in a submission queue entry (SQE) to be submitted to the Linux kernel. It allocates space on a file without writing any data to the file.

Syntax

io_uring_prep_fallocate(struct io_uring_sqe *sqe,
                        int fd,
                        int mode,
                        off_t offset,
                        off_t len,
                        unsigned flags);

Options/Flags

  • fd: File descriptor of the target file.
  • mode: Allocation mode, typically one of the following:
    • FALLOC_FL_KEEP_SIZE: Keep the file size unchanged.
    • FALLOC_FL_PUNCH_HOLE: Punch a hole at the specified location.
  • offset: Starting offset of the allocation.
  • len: Length of the allocation.
  • flags: Miscellaneous flags, typically used for setting file system-specific options.

Examples

Allocate space at the end of a file:

struct io_uring_sqe *sqe = io_uring_get_sqe(ring);
io_uring_prep_fallocate(sqe, fd, FALLOC_FL_KEEP_SIZE, 0, 1024, 0);
io_uring_submit(ring);
io_uring_wait_cqe(ring, &cqe);

Punch a hole in a file:

io_uring_prep_fallocate(sqe, fd, FALLOC_FL_PUNCH_HOLE, 512, 1024, 0);

Common Issues

  • Argument validation: Negative or invalid values for parameters may result in errors.
  • File permissions: Ensure the file has appropriate permissions for the requested operation.
  • File system support: Not all file systems support the fallocate operation. Verify support before using it.

Integration

io_uring_prep_fallocate can be integrated into custom applications or libraries that use the io_uring API for high-performance I/O operations.

Related Commands

  • fallocate(2): Standard C library function for file allocation.
  • posix_fallocate(3): POSIX-compliant file allocation function.