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‘seek’ now accepts ‘SEEK_DATA’ and ‘SEEK_HOLE’ where supported.

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* libguile/ports.c (scm_seek): Let SEEK_DATA and SEEK_HOLE through.
(scm_init_ice_9_ports): Define ‘SEEK_DATA’ and ‘SEEK_HOLE’.
* module/ice-9/ports.scm: Export ‘SEEK_DATA’ and ‘SEEK_HOLE’ when
defined.
* test-suite/tests/ports.test ("size of sparse file")
("SEEK_DATA while on data", "SEEK_DATA while in hole")
("SEEK_HOLE while in hole"): New tests.
* NEWS: Update.
This commit is contained in:
Ludovic Courtès 2024-04-15 19:48:10 +02:00
parent 4a0c2433d9
commit 696acfc9e5
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5 changed files with 119 additions and 10 deletions
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22
doc/ref/api-io.texi
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@ -823,8 +823,26 @@ Seek from the current position.
@defvar SEEK_END
Seek from the end of the file.
@end defvar
If @var{fd_port} is a file descriptor, the underlying system
call is @code{lseek}. @var{port} may be a string port.
On systems that support it, such as GNU/Linux, the following
constants can be used for @var{whence} to navigate ``holes'' in
sparse files:
@defvar SEEK_DATA
Seek to the next location in the file greater than or equal to
@var{offset} containing data. If @var{offset} points to data,
then the file offset is set to @var{offset}.
@end defvar
@defvar SEEK_HOLE
Seek to the next hole in the file greater than or equal to the
@var{offset}. If @var{offset} points into the middle of a hole,
then the file offset is set to @var{offset}. If there is no hole
past @var{offset}, then the file offset is adjusted to the end of
the file---i.e., there is an implicit hole at the end of any file.
@end defvar
If @var{fd_port} is a file descriptor, the underlying system call
is @code{lseek} (@pxref{File Position Primitive,,, libc, The GNU C
Library Reference Manual}). @var{port} may be a string port.
The value returned is the new position in @var{fd_port}. This means
that the current position of a port can be obtained using: