vmsplice

vmsplice is a system call in Linux that allows a user-space process to directly splice data from a memory buffer into a pipe or vice-versa, without copying the data. This is achieved by mapping the user-space buffer into the kernel's address space and then linking it to the pipe's internal buffer. This avoids the overhead of user-space to kernel-space copying, which can be significant for large data transfers.

The primary benefit of vmsplice is improved performance, particularly in scenarios involving frequent and large data transfers between user space and kernel space, such as in network applications or high-performance data processing. By eliminating the data copy, vmsplice reduces CPU usage and memory bandwidth consumption.

vmsplice takes three arguments: a file descriptor representing the pipe, a pointer to the user-space buffer, and the number of bytes to splice. It returns the number of bytes successfully spliced. It can be used in conjunction with other splice-related system calls to create efficient data pipelines.

However, vmsplice has some limitations. It is only available on Linux and requires specific kernel support. Also, the mapped user-space buffer remains inaccessible to the user-space process while it is mapped into the kernel, meaning the process cannot modify or read from that buffer during the splice operation. Despite these limitations, vmsplice remains a valuable tool for optimizing performance-critical I/O operations on Linux systems.