preadv

preadv is a system call used in Unix-like operating systems to read data from a file descriptor into multiple buffers. It is an extension of the standard read() system call and is particularly useful when dealing with data that is naturally fragmented or when optimizing I/O operations. The "v" in preadv stands for "vector," indicating that it operates on an array of iovec structures, where each iovec describes a buffer and its corresponding size.

The primary advantage of preadv over multiple individual read() calls is efficiency. By allowing the kernel to scatter data directly into multiple memory locations in a single operation, it reduces the overhead associated with system call context switching and data copying. This can lead to significant performance improvements, especially in applications that frequently read large amounts of data into different parts of memory.

preadv takes the file descriptor, a pointer to an array of iovec structures, the number of iovec structures in the array, and an offset into the file from which to start reading. The offset parameter allows for non-sequential reads without modifying the file descriptor's current position. This is a key difference from the standard read() call, which reads from the current file offset.

This system call is often found in high-performance networking applications, database systems, and other I/O-intensive software where optimizing data transfer is critical. Its ability to read into multiple buffers simultaneously and specify an offset makes it a powerful tool for developers looking to fine-tune their application's performance.