llseek - move extended read/write file pointer
#include <sys/types.h> #include <unistd.h> offset_t llseek(int fildes, offset_t offset, int whence);
The llseek() function sets the 64-bit extended file pointer associated with the open file descriptor specified by fildes as follows:
A "hole" is defined as a contiguous range of bytes in a file, all having the value of zero, but not all zeros in a file are guaranteed to be represented as holes returned with SEEK_HOLE. Filesystems are allowed to expose ranges of zeros with SEEK_HOLE, but not required to. Applications can use SEEK_HOLE to optimise their behavior for ranges of zeros, but must not depend on it to find all such ranges in a file. The existence of a hole at the end of every data region allows for easy programming and implies that a virtual hole exists at the end of the file.
For filesystems that do not supply information about holes, the file will be represented as one entire data region.
Although each file has a 64-bit file pointer associated with it, some existing file system types (such as tmpfs) do not support the full range of 64-bit offsets. In particular, on such file systems, non-device files remain limited to offsets of less than two gigabytes. Device drivers may support offsets of up to 1024 gigabytes for device special files.
Some devices are incapable of seeking. The value of the file pointer associated with such a device is undefined.
Upon successful completion, llseek() returns the resulting pointer location as measured in bytes from the beginning of the file. Remote file descriptors are the only ones that allow negative file pointers. Otherwise, -1 is returned, the file pointer remains unchanged, and errno is set to indicate the error.
The llseek() function will fail if:
creat(2), dup(2), fcntl(2), lseek(2), open(2)
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Created 1996-2021 by Maxim Chirkov
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