X-Git-Url: https://git.saurik.com/apple/xnu.git/blobdiff_plain/3903760236c30e3b5ace7a4eefac3a269d68957c..0a7de7458d150b5d4dffc935ba399be265ef0a1a:/bsd/man/man2/lseek.2 diff --git a/bsd/man/man2/lseek.2 b/bsd/man/man2/lseek.2 index 6d29d53b0..d5bea0b62 100644 --- a/bsd/man/man2/lseek.2 +++ b/bsd/man/man2/lseek.2 @@ -91,6 +91,23 @@ the offset is set to the size of the file plus .Fa offset bytes. +.It +If +.Fa whence +is +.Dv SEEK_HOLE , +the offset is set to the start of the next hole greater than or equal +to the supplied +.Fa offset . +The definition of a hole is provided below. +.It +If +.Fa whence +is +.Dv SEEK_DATA , +the offset is set to the start of the next non-hole file region greater +than or equal to the supplied +.Fa offset . .El .Pp The @@ -102,6 +119,39 @@ bytes of zeros (until data is actually written into the gap). .Pp Some devices are incapable of seeking. The value of the pointer associated with such a device is undefined. +.Pp +A +.Qq 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 +.Dv SEEK_HOLE . +File systems are allowed to expose ranges of zeros with +.Dv SEEK_HOLE , +but not required to. +Applications can use +.Dv SEEK_HOLE +to optimise their behavior for ranges of zeros, but must not depend on it to +find all such ranges in a file. +Each file is presented as having a zero-size virtual hole at the very +end of the file. +The existence of a hole at the end of every data region allows for easy +programming and also provides compatibility to the original implementation +in Solaris. +It also causes the current file size (i.e., end-of-file offset) to be returned +to indicate that there are no more holes past the supplied +.Fa offset . +Applications should use +.Fn fpathconf _PC_MIN_HOLE_SIZE +or +.Fn pathconf _PC_MIN_HOLE_SIZE +to determine if a file system supports +.Dv SEEK_HOLE . +See +.Xr pathconf 2 . +.Pp +For file systems that do not supply information about holes, the file will be +represented as one entire data region. .Sh RETURN VALUES Upon successful completion, .Fn lseek @@ -132,6 +182,15 @@ and .Fa whence ) is negative. .\" ========== +.It Bq Er ENXIO +For +.Dv SEEK_DATA , +there are no more data regions past the supplied offset. +Due to existence of the hole at the end of the file, for +.Dv SEEK_HOLE +this error is only returned when the +.Fa offset +already points to the end-of-file position. .It Bq Er EOVERFLOW The seek location is too large to be stored in an object of type off_t.