[ViewVC] Diff of: cvs/IO-AIO/AIO.pm

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.240 by root, Mon Dec 17 06:18:39 2012 UTC vs.
Revision 1.282 by root, Tue Feb 20 05:23:47 2018 UTC

 =head1 NAME
-IO::AIO - Asynchronous Input/Output
+IO::AIO - Asynchronous/Advanced Input/Output
 =head1 SYNOPSIS
  use IO::AIO;
 not well-supported or restricted (GNU/Linux doesn't allow them on normal
 files currently, for example), and they would only support aio_read and
 aio_write, so the remaining functionality would have to be implemented
 using threads anyway.
+In addition to asynchronous I/O, this module also exports some rather
+arcane interfaces, such as C<madvise> or linux's C<splice> system call,
+which is why the C<A> in C<AIO> can also mean I<advanced>.
 Although the module will work in the presence of other (Perl-) threads,
 it is currently not reentrant in any way, so use appropriate locking
 yourself, always call C<poll_cb> from within the same thread, or never
 call C<poll_cb> (or other C<aio_> functions) recursively.
 =head2 EXAMPLE
 This is a simple example that uses the EV module and loads
 F</etc/passwd> asynchronously:
-   use Fcntl;
    use EV;
    use IO::AIO;
    # register the IO::AIO callback with EV
    my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
          # file contents now in $contents
          print $contents;
          # exit event loop and program
-         EV::unloop;
+         EV::break;
       };
    };
    # possibly queue up other requests, or open GUI windows,
    # check for sockets etc. etc.
    # process events as long as there are some:
-   EV::loop;
+   EV::run;
 =head1 REQUEST ANATOMY AND LIFETIME
 Every C<aio_*> function creates a request. which is a C data structure not
 directly visible to Perl.
 use common::sense;
 use base 'Exporter';
 BEGIN {
-   our $VERSION = '4.18';
+   our $VERSION = 4.4;
    our @AIO_REQ = qw(aio_sendfile aio_seek aio_read aio_write aio_open aio_close
                      aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_readdirx
-                     aio_scandir aio_symlink aio_readlink aio_realpath aio_sync
+                     aio_scandir aio_symlink aio_readlink aio_realpath aio_fcntl aio_ioctl
-                     aio_fsync aio_syncfs aio_fdatasync aio_sync_file_range aio_allocate
+                     aio_sync aio_fsync aio_syncfs aio_fdatasync aio_sync_file_range
-                     aio_pathsync aio_readahead aio_fiemap
+                     aio_pathsync aio_readahead aio_fiemap aio_allocate
-                     aio_rename aio_link aio_move aio_copy aio_group
+                     aio_rename aio_rename2 aio_link aio_move aio_copy aio_group
                      aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown
                      aio_chmod aio_utime aio_truncate
                      aio_msync aio_mtouch aio_mlock aio_mlockall
                      aio_statvfs
+                     aio_slurp
                      aio_wd);
    our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
    our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
                        min_parallel max_parallel max_idle idle_timeout
    aio_unlink $pathname, $callback->($status)
    aio_mknod $pathname, $mode, $dev, $callback->($status)
    aio_link $srcpath, $dstpath, $callback->($status)
    aio_symlink $srcpath, $dstpath, $callback->($status)
    aio_readlink $pathname, $callback->($link)
-   aio_realpath $pathname, $callback->($link)
+   aio_realpath $pathname, $callback->($path)
    aio_rename $srcpath, $dstpath, $callback->($status)
+   aio_rename2 $srcpath, $dstpath, $flags, $callback->($status)
    aio_mkdir $pathname, $mode, $callback->($status)
    aio_rmdir $pathname, $callback->($status)
    aio_readdir $pathname, $callback->($entries)
    aio_readdirx $pathname, $flags, $callback->($entries, $flags)
       IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
    aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
    aio_load $pathname, $data, $callback->($status)
    aio_copy $srcpath, $dstpath, $callback->($status)
    aio_move $srcpath, $dstpath, $callback->($status)
    aio_rmtree $pathname, $callback->($status)
+   aio_fcntl $fh, $cmd, $arg, $callback->($status)
+   aio_ioctl $fh, $request, $buf, $callback->($status)
    aio_sync $callback->($status)
    aio_syncfs $fh, $callback->($status)
    aio_fsync $fh, $callback->($status)
    aio_fdatasync $fh, $callback->($status)
    aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
    aio_pathsync $pathname, $callback->($status)
-   aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
+   aio_msync $scalar, $offset = 0, $length = undef, flags = MS_SYNC, $callback->($status)
    aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
    aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
    aio_mlockall $flags, $callback->($status)
    aio_group $callback->(...)
    aio_nop $callback->()
    IO::AIO::idle_timeout $seconds
    IO::AIO::max_outstanding $maxreqs
    IO::AIO::nreqs
    IO::AIO::nready
    IO::AIO::npending
+   $nfd = IO::AIO::get_fdlimit [EXPERIMENTAL]
+   IO::AIO::min_fdlimit $nfd [EXPERIMENTAL]
    IO::AIO::sendfile $ofh, $ifh, $offset, $count
    IO::AIO::fadvise $fh, $offset, $len, $advice
    IO::AIO::mmap $scalar, $length, $prot, $flags[, $fh[, $offset]]
    IO::AIO::munmap $scalar
 following POSIX and non-POSIX constants are available (missing ones on
 your system are, as usual, C<0>):
 C<O_ASYNC>, C<O_DIRECT>, C<O_NOATIME>, C<O_CLOEXEC>, C<O_NOCTTY>, C<O_NOFOLLOW>,
 C<O_NONBLOCK>, C<O_EXEC>, C<O_SEARCH>, C<O_DIRECTORY>, C<O_DSYNC>,
-C<O_RSYNC>, C<O_SYNC> and C<O_TTY_INIT>.
+C<O_RSYNC>, C<O_SYNC>, C<O_PATH>, C<O_TMPFILE>, and C<O_TTY_INIT>.
 =item aio_close $fh, $callback->($status)
 Asynchronously close a file and call the callback with the result
 =item aio_read  $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
 =item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
 Reads or writes C<$length> bytes from or to the specified C<$fh> and
-C<$offset> into the scalar given by C<$data> and offset C<$dataoffset>
+C<$offset> into the scalar given by C<$data> and offset C<$dataoffset> and
-and calls the callback without the actual number of bytes read (or -1 on
+calls the callback with the actual number of bytes transferred (or -1 on
 error, just like the syscall).
 C<aio_read> will, like C<sysread>, shrink or grow the C<$data> scalar to
 offset plus the actual number of bytes read.
 As native sendfile syscalls (as practically any non-POSIX interface hacked
 together in a hurry to improve benchmark numbers) tend to be rather buggy
 on many systems, this implementation tries to work around some known bugs
 in Linux and FreeBSD kernels (probably others, too), but that might fail,
 so you really really should check the return value of C<aio_sendfile> -
-fewre bytes than expected might have been transferred.
+fewer bytes than expected might have been transferred.
 =item aio_readahead $fh,$offset,$length, $callback->($retval)
 C<aio_readahead> populates the page cache with data from a file so that
 whole pages, so that offset is effectively rounded down to a page boundary
 and bytes are read up to the next page boundary greater than or equal to
 (off-set+length). C<aio_readahead> does not read beyond the end of the
 file. The current file offset of the file is left unchanged.
-If that syscall doesn't exist (likely if your OS isn't Linux) it will be
+If that syscall doesn't exist (likely if your kernel isn't Linux) it will
-emulated by simply reading the data, which would have a similar effect.
+be emulated by simply reading the data, which would have a similar effect.
 =item aio_stat  $fh_or_path, $callback->($status)
 =item aio_lstat $fh, $callback->($status)
       namemax => 255,
       frsize  => 1024,
       fsid    => 1810
    }
-Here is a (likely partial) list of fsid values used by Linux - it is safe
-to hardcode these when the $^O is C<linux>:
-   0x0000adf5 adfs
-   0x0000adff affs
-   0x5346414f afs
-   0x09041934 anon-inode filesystem
-   0x00000187 autofs
-   0x42465331 befs
-   0x1badface bfs
-   0x42494e4d binfmt_misc
-   0x9123683e btrfs
-   0x0027e0eb cgroupfs
-   0xff534d42 cifs
-   0x73757245 coda
-   0x012ff7b7 coh
-   0x28cd3d45 cramfs
-   0x453dcd28 cramfs-wend (wrong endianness)
-   0x64626720 debugfs
-   0x00001373 devfs
-   0x00001cd1 devpts
-   0x0000f15f ecryptfs
-   0x00414a53 efs
-   0x0000137d ext
-   0x0000ef53 ext2/ext3
-   0x0000ef51 ext2
-   0x00004006 fat
-   0x65735546 fuseblk
-   0x65735543 fusectl
-   0x0bad1dea futexfs
-   0x01161970 gfs2
-   0x47504653 gpfs
-   0x00004244 hfs
-   0xf995e849 hpfs
-   0x958458f6 hugetlbfs
-   0x2bad1dea inotifyfs
-   0x00009660 isofs
-   0x000072b6 jffs2
-   0x3153464a jfs
-   0x6b414653 k-afs
-   0x0bd00bd0 lustre
-   0x0000137f minix
-   0x0000138f minix 30 char names
-   0x00002468 minix v2
-   0x00002478 minix v2 30 char names
-   0x00004d5a minix v3
-   0x19800202 mqueue
-   0x00004d44 msdos
-   0x0000564c novell
-   0x00006969 nfs
-   0x6e667364 nfsd
-   0x00003434 nilfs
-   0x5346544e ntfs
-   0x00009fa1 openprom
-   0x7461636F ocfs2
-   0x00009fa0 proc
-   0x6165676c pstorefs
-   0x0000002f qnx4
-   0x858458f6 ramfs
-   0x52654973 reiserfs
-   0x00007275 romfs
-   0x67596969 rpc_pipefs
-   0x73636673 securityfs
-   0xf97cff8c selinux
-   0x0000517b smb
-   0x534f434b sockfs
-   0x73717368 squashfs
-   0x62656572 sysfs
-   0x012ff7b6 sysv2
-   0x012ff7b5 sysv4
-   0x01021994 tmpfs
-   0x15013346 udf
-   0x00011954 ufs
-   0x54190100 ufs byteswapped
-   0x00009fa2 usbdevfs
-   0x01021997 v9fs
-   0xa501fcf5 vxfs
-   0xabba1974 xenfs
-   0x012ff7b4 xenix
-   0x58465342 xfs
-   0x012fd16d xia
 =item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
 Works like perl's C<utime> function (including the special case of $atime
 and $mtime being undef). Fractional times are supported if the underlying
 syscalls support them.
 Works like truncate(2) or ftruncate(2).
 =item aio_allocate $fh, $mode, $offset, $len, $callback->($status)
-Allocates or freed disk space according to the C<$mode> argument. See the
+Allocates or frees disk space according to the C<$mode> argument. See the
-linux C<fallocate> docuemntation for details.
+linux C<fallocate> documentation for details.
-C<$mode> can currently be C<0> or C<IO::AIO::FALLOC_FL_KEEP_SIZE>
+C<$mode> is usually C<0> or C<IO::AIO::FALLOC_FL_KEEP_SIZE> to allocate
-to allocate space, or C<IO::AIO::FALLOC_FL_PUNCH_HOLE |
+space, or C<IO::AIO::FALLOC_FL_PUNCH_HOLE | IO::AIO::FALLOC_FL_KEEP_SIZE>,
-IO::AIO::FALLOC_FL_KEEP_SIZE>, to deallocate a file range.
+to deallocate a file range.
+IO::AIO also supports C<FALLOC_FL_COLLAPSE_RANGE>, to remove a range
+(without leaving a hole), C<FALLOC_FL_ZERO_RANGE>, to zero a range,
+C<FALLOC_FL_INSERT_RANGE> to insert a range and C<FALLOC_FL_UNSHARE_RANGE>
+to unshare shared blocks (see your L<fallocate(2)> manpage).
 The file system block size used by C<fallocate> is presumably the
-C<f_bsize> returned by C<statvfs>.
+C<f_bsize> returned by C<statvfs>, but different filesystems and filetypes
+can dictate other limitations.
 If C<fallocate> isn't available or cannot be emulated (currently no
 emulation will be attempted), passes C<-1> and sets C<$!> to C<ENOSYS>.
 =item aio_rename $srcpath, $dstpath, $callback->($status)
 Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
 rename(2) and call the callback with the result code.
+On systems that support the AIO::WD working directory abstraction
+natively, the case C<[$wd, "."]> as C<$srcpath> is specialcased - instead
+of failing, C<rename> is called on the absolute path of C<$wd>.
+=item aio_rename2 $srcpath, $dstpath, $flags, $callback->($status)
+Basically a version of C<aio_rename> with an additional C<$flags>
+argument. Calling this with C<$flags=0> is the same as calling
+C<aio_rename>.
+Non-zero flags are currently only supported on GNU/Linux systems that
+support renameat2. Other systems fail with C<ENOSYS> in this case.
+The following constants are available (missing ones are, as usual C<0>),
+see renameat2(2) for details:
+C<IO::AIO::RENAME_NOREPLACE>, C<IO::AIO::RENAME_EXCHANGE>
+and C<IO::AIO::RENAME_WHITEOUT>.
 =item aio_mkdir $pathname, $mode, $callback->($status)
 Asynchronously mkdir (create) a directory and call the callback with
 the result code. C<$mode> will be modified by the umask at the time the
 =item aio_rmdir $pathname, $callback->($status)
 Asynchronously rmdir (delete) a directory and call the callback with the
 result code.
+On systems that support the AIO::WD working directory abstraction
+natively, the case C<[$wd, "."]> is specialcased - instead of failing,
+C<rmdir> is called on the absolute path of C<$wd>.
 =item aio_readdir $pathname, $callback->($entries)
 Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
 C<$type>'s are known, which can be used to speed up some algorithms.
 =back
+=item aio_slurp $pathname, $offset, $length, $data, $callback->($status)
+Opens, reads and closes the given file. The data is put into C<$data>,
+which is resized as required.
+If C<$offset> is negative, then it is counted from the end of the file.
+If C<$length> is zero, then the remaining length of the file is
+used. Also, in this case, the same limitations to modifying C<$data> apply
+as when IO::AIO::mmap is used, i.e. it must only be modified in-place
+with C<substr>. If the size of the file is known, specifying a non-zero
+C<$length> results in a performance advantage.
+This request is similar to the older C<aio_load> request, but since it is
+a single request, it might be more efficient to use.
+Example: load F</etc/passwd> into C<$passwd>.
+   my $passwd;
+   aio_slurp "/etc/passwd", 0, 0, $passwd, sub {
+      $_[0] >= 0
+         or die "/etc/passwd: $!\n";
+      printf "/etc/passwd is %d bytes long, and contains:\n", length $passwd;
+      print $passwd;
+   };
+   IO::AIO::flush;
 =item aio_load $pathname, $data, $callback->($status)
 This is a composite request that tries to fully load the given file into
 memory. Status is the same as with aio_read.
+Using C<aio_slurp> might be more efficient, as it is a single request.
 =cut
 sub aio_load($$;$) {
    my ($path, undef, $cb) = @_;
 =item aio_copy $srcpath, $dstpath, $callback->($status)
 Try to copy the I<file> (directories not supported as either source or
 destination) from C<$srcpath> to C<$dstpath> and call the callback with
 a status of C<0> (ok) or C<-1> (error, see C<$!>).
+Existing destination files will be truncated.
 This is a composite request that creates the destination file with
 mode 0200 and copies the contents of the source file into it using
 C<aio_sendfile>, followed by restoring atime, mtime, access mode and
 uid/gid, in that order.
 Scans a directory (similar to C<aio_readdir>) but additionally tries to
 efficiently separate the entries of directory C<$path> into two sets of
 names, directories you can recurse into (directories), and ones you cannot
 recurse into (everything else, including symlinks to directories).
-C<aio_scandir> is a composite request that creates of many sub requests_
+C<aio_scandir> is a composite request that generates many sub requests.
 C<$maxreq> specifies the maximum number of outstanding aio requests that
 this function generates. If it is C<< <= 0 >>, then a suitable default
 will be chosen (currently 4).
 On error, the callback is called without arguments, otherwise it receives
    };
    $grp
 }
+=item aio_fcntl $fh, $cmd, $arg, $callback->($status)
+=item aio_ioctl $fh, $request, $buf, $callback->($status)
+These work just like the C<fcntl> and C<ioctl> built-in functions, except
+they execute asynchronously and pass the return value to the callback.
+Both calls can be used for a lot of things, some of which make more sense
+to run asynchronously in their own thread, while some others make less
+sense. For example, calls that block waiting for external events, such
+as locking, will also lock down an I/O thread while it is waiting, which
+can deadlock the whole I/O system. At the same time, there might be no
+alternative to using a thread to wait.
+So in general, you should only use these calls for things that do
+(filesystem) I/O, not for things that wait for other events (network,
+other processes), although if you are careful and know what you are doing,
+you still can.
+The following constants are available (missing ones are, as usual C<0>):
+C<F_DUPFD_CLOEXEC>,
+C<F_OFD_GETLK>, C<F_OFD_SETLK>, C<F_OFD_GETLKW>,
+C<FIFREEZE>, C<FITHAW>, C<FITRIM>, C<FICLONE>, C<FICLONERANGE>, C<FIDEDUPERANGE>.
+C<FS_IOC_GETFLAGS>, C<FS_IOC_SETFLAGS>, C<FS_IOC_GETVERSION>, C<FS_IOC_SETVERSION>,
+C<FS_IOC_FIEMAP>.
+C<FS_IOC_FSGETXATTR>, C<FS_IOC_FSSETXATTR>, C<FS_IOC_SET_ENCRYPTION_POLICY>,
+C<FS_IOC_GET_ENCRYPTION_PWSALT>, C<FS_IOC_GET_ENCRYPTION_POLICY>, C<FS_KEY_DESCRIPTOR_SIZE>.
+C<FS_SECRM_FL>, C<FS_UNRM_FL>, C<FS_COMPR_FL>, C<FS_SYNC_FL>, C<FS_IMMUTABLE_FL>,
+C<FS_APPEND_FL>, C<FS_NODUMP_FL>, C<FS_NOATIME_FL>, C<FS_DIRTY_FL>,
+C<FS_COMPRBLK_FL>, C<FS_NOCOMP_FL>, C<FS_ENCRYPT_FL>, C<FS_BTREE_FL>,
+C<FS_INDEX_FL>, C<FS_JOURNAL_DATA_FL>, C<FS_NOTAIL_FL>, C<FS_DIRSYNC_FL>, C<FS_TOPDIR_FL>,
+C<FS_FL_USER_MODIFIABLE>.
+C<FS_XFLAG_REALTIME>, C<FS_XFLAG_PREALLOC>, C<FS_XFLAG_IMMUTABLE>, C<FS_XFLAG_APPEND>,
+C<FS_XFLAG_SYNC>, C<FS_XFLAG_NOATIME>, C<FS_XFLAG_NODUMP>, C<FS_XFLAG_RTINHERIT>,
+C<FS_XFLAG_PROJINHERIT>, C<FS_XFLAG_NOSYMLINKS>, C<FS_XFLAG_EXTSIZE>, C<FS_XFLAG_EXTSZINHERIT>,
+C<FS_XFLAG_NODEFRAG>, C<FS_XFLAG_FILESTREAM>, C<FS_XFLAG_DAX>, C<FS_XFLAG_HASATTR>,
 =item aio_sync $callback->($status)
 Asynchronously call sync and call the callback when finished.
 =item aio_fsync $fh, $callback->($status)
    };
    $grp
 }
-=item aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
+=item aio_msync $scalar, $offset = 0, $length = undef, flags = MS_SYNC, $callback->($status)
 This is a rather advanced IO::AIO call, which only works on mmap(2)ed
 scalars (see the C<IO::AIO::mmap> function, although it also works on data
 scalars managed by the L<Sys::Mmap> or L<Mmap> modules, note that the
 scalar must only be modified in-place while an aio operation is pending on
 It calls the C<msync> function of your OS, if available, with the memory
 area starting at C<$offset> in the string and ending C<$length> bytes
 later. If C<$length> is negative, counts from the end, and if C<$length>
 is C<undef>, then it goes till the end of the string. The flags can be
-a combination of C<IO::AIO::MS_ASYNC>, C<IO::AIO::MS_INVALIDATE> and
+either C<IO::AIO::MS_ASYNC> or C<IO::AIO::MS_SYNC>, plus an optional
-C<IO::AIO::MS_SYNC>.
+C<IO::AIO::MS_INVALIDATE>.
 =item aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
 This is a rather advanced IO::AIO call, which works best on mmap(2)ed
 scalars.
 C<IO::AIO::FIEMAP_EXTENT_DATA_ENCRYPTED>, C<IO::AIO::FIEMAP_EXTENT_NOT_ALIGNED>,
 C<IO::AIO::FIEMAP_EXTENT_DATA_INLINE>, C<IO::AIO::FIEMAP_EXTENT_DATA_TAIL>,
 C<IO::AIO::FIEMAP_EXTENT_UNWRITTEN>, C<IO::AIO::FIEMAP_EXTENT_MERGED> or
 C<IO::AIO::FIEMAP_EXTENT_SHARED>.
-At the time of this writing (Linux 3.2), this requets is unreliable unless
+At the time of this writing (Linux 3.2), this request is unreliable unless
 C<$count> is C<undef>, as the kernel has all sorts of bugs preventing
-it to return all extents of a range for files with large number of
+it to return all extents of a range for files with a large number of
-extents. The code works around all these issues if C<$count> is undef.
+extents. The code (only) works around all these issues if C<$count> is
+C<undef>.
 =item aio_group $callback->(...)
 This is a very special aio request: Instead of doing something, it is a
 container for other aio requests, which is useful if you want to bundle
       aio_stat [$etcdir, "passwd"], sub {
          # yay
       };
    };
-That C<aio_wd> is a request and not a normal function shows that creating
+The fact that C<aio_wd> is a request and not a normal function shows that
-an IO::AIO::WD object is itself a potentially blocking operation, which is
+creating an IO::AIO::WD object is itself a potentially blocking operation,
-why it is done asynchronously.
+which is why it is done asynchronously.
 To stat the directory obtained with C<aio_wd> above, one could write
 either of the following three request calls:
    aio_lstat "/etc"    , sub { ...  # pathname as normal string
 There are some caveats: when directories get renamed (or deleted), the
 pathname string doesn't change, so will point to the new directory (or
 nowhere at all), while the directory fd, if available on the system,
 will still point to the original directory. Most functions accepting a
 pathname will use the directory fd on newer systems, and the string on
-older systems. Some functions (such as realpath) will always rely on the
+older systems. Some functions (such as C<aio_realpath>) will always rely on
-string form of the pathname.
+the string form of the pathname.
 So this functionality is mainly useful to get some protection against
 C<chdir>, to easily get an absolute path out of a relative path for future
 reference, and to speed up doing many operations in the same directory
 (e.g. when stat'ing all files in a directory).
 passing C<undef> as working directory component of a pathname fails the
 request with C<ENOENT>, there is often no need for error checking in the
 C<aio_wd> callback, as future requests using the value will fail in the
 expected way.
-If this call isn't available because your OS lacks it or it couldn't be
-detected, it will be emulated by calling C<fsync> instead.
 =item IO::AIO::CWD
 This is a compiletime constant (object) that represents the process
 current working directory.
    aio_realpath $wd, sub {
       warn "path is $_[0]\n";
    };
+Currently, C<aio_statvfs> always, and C<aio_rename> and C<aio_rmdir>
+sometimes, fall back to using an absolue path.
 =head2 IO::AIO::REQ CLASS
 All non-aggregate C<aio_*> functions return an object of this class when
 called in non-void context.
 This is a very bad function to use in interactive programs because it
 blocks, and a bad way to reduce concurrency because it is inexact: Better
 use an C<aio_group> together with a feed callback.
-It's main use is in scripts without an event loop - when you want to stat
+Its main use is in scripts without an event loop - when you want to stat
-a lot of files, you can write somehting like this:
+a lot of files, you can write something like this:
    IO::AIO::max_outstanding 32;
    for my $path (...) {
       aio_stat $path , ...;
 =back
 =head3 MISCELLANEOUS FUNCTIONS
-IO::AIO implements some functions that might be useful, but are not
+IO::AIO implements some functions that are useful when you want to use
-asynchronous.
+some "Advanced I/O" function not available to in Perl, without going the
+"Asynchronous I/O" route. Many of these have an asynchronous C<aio_*>
+counterpart.
 =over 4
+=item $numfd = IO::AIO::get_fdlimit
+This function is I<EXPERIMENTAL> and subject to change.
+Tries to find the current file descriptor limit and returns it, or
+C<undef> and sets C<$!> in case of an error. The limit is one larger than
+the highest valid file descriptor number.
+=item IO::AIO::min_fdlimit [$numfd]
+This function is I<EXPERIMENTAL> and subject to change.
+Try to increase the current file descriptor limit(s) to at least C<$numfd>
+by changing the soft or hard file descriptor resource limit. If C<$numfd>
+is missing, it will try to set a very high limit, although this is not
+recommended when you know the actual minimum that you require.
+If the limit cannot be raised enough, the function makes a best-effort
+attempt to increase the limit as much as possible, using various
+tricks, while still failing. You can query the resulting limit using
+C<IO::AIO::get_fdlimit>.
+If an error occurs, returns C<undef> and sets C<$!>, otherwise returns
+true.
 =item IO::AIO::sendfile $ofh, $ifh, $offset, $count
 Calls the C<eio_sendfile_sync> function, which is like C<aio_sendfile>,
 but is blocking (this makes most sense if you know the input data is
 =item IO::AIO::madvise $scalar, $offset, $len, $advice
 Simply calls the C<posix_madvise> function (see its
 manpage for details). The following advice constants are
 available: C<IO::AIO::MADV_NORMAL>, C<IO::AIO::MADV_SEQUENTIAL>,
-C<IO::AIO::MADV_RANDOM>, C<IO::AIO::MADV_WILLNEED>, C<IO::AIO::MADV_DONTNEED>.
+C<IO::AIO::MADV_RANDOM>, C<IO::AIO::MADV_WILLNEED>,
+C<IO::AIO::MADV_DONTNEED>.
+If C<$offset> is negative, counts from the end. If C<$length> is negative,
+the remaining length of the C<$scalar> is used. If possible, C<$length>
+will be reduced to fit into the C<$scalar>.
 On systems that do not implement C<posix_madvise>, this function returns
 ENOSYS, otherwise the return value of C<posix_madvise>.
 =item IO::AIO::mprotect $scalar, $offset, $len, $protect
 Simply calls the C<mprotect> function on the preferably AIO::mmap'ed
 $scalar (see its manpage for details). The following protect
 constants are available: C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_READ>,
 C<IO::AIO::PROT_WRITE>, C<IO::AIO::PROT_EXEC>.
+If C<$offset> is negative, counts from the end. If C<$length> is negative,
+the remaining length of the C<$scalar> is used. If possible, C<$length>
+will be reduced to fit into the C<$scalar>.
 On systems that do not implement C<mprotect>, this function returns
 ENOSYS, otherwise the return value of C<mprotect>.
 =item IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
 Memory-maps a file (or anonymous memory range) and attaches it to the
 given C<$scalar>, which will act like a string scalar. Returns true on
 success, and false otherwise.
+The scalar must exist, but its contents do not matter - this means you
+cannot use a nonexistant array or hash element. When in doubt, C<undef>
+the scalar first.
-The only operations allowed on the scalar are C<substr>/C<vec> that don't
+The only operations allowed on the mmapped scalar are C<substr>/C<vec>,
-change the string length, and most read-only operations such as copying it
+which don't change the string length, and most read-only operations such
-or searching it with regexes and so on.
+as copying it or searching it with regexes and so on.
 Anything else is unsafe and will, at best, result in memory leaks.
 The memory map associated with the C<$scalar> is automatically removed
-when the C<$scalar> is destroyed, or when the C<IO::AIO::mmap> or
+when the C<$scalar> is undef'd or destroyed, or when the C<IO::AIO::mmap>
-C<IO::AIO::munmap> functions are called.
+or C<IO::AIO::munmap> functions are called on it.
 This calls the C<mmap>(2) function internally. See your system's manual
 page for details on the C<$length>, C<$prot> and C<$flags> parameters.
 The C<$length> must be larger than zero and smaller than the actual
 filesize.
 C<$prot> is a combination of C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_EXEC>,
 C<IO::AIO::PROT_READ> and/or C<IO::AIO::PROT_WRITE>,
-C<$flags> can be a combination of C<IO::AIO::MAP_SHARED> or
+C<$flags> can be a combination of
-C<IO::AIO::MAP_PRIVATE>, or a number of system-specific flags (when
+C<IO::AIO::MAP_SHARED> or
-not available, the are defined as 0): C<IO::AIO::MAP_ANONYMOUS>
+C<IO::AIO::MAP_PRIVATE>,
+or a number of system-specific flags (when not available, the are C<0>):
-(which is set to C<MAP_ANON> if your system only provides this
+C<IO::AIO::MAP_ANONYMOUS> (which is set to C<MAP_ANON> if your system only provides this constant),
-constant), C<IO::AIO::MAP_HUGETLB>, C<IO::AIO::MAP_LOCKED>,
+C<IO::AIO::MAP_LOCKED>,
-C<IO::AIO::MAP_NORESERVE>, C<IO::AIO::MAP_POPULATE> or
+C<IO::AIO::MAP_NORESERVE>,
+C<IO::AIO::MAP_POPULATE>,
-C<IO::AIO::MAP_NONBLOCK>
+C<IO::AIO::MAP_NONBLOCK>,
+C<IO::AIO::MAP_FIXED>,
+C<IO::AIO::MAP_GROWSDOWN>,
+C<IO::AIO::MAP_32BIT>,
+C<IO::AIO::MAP_HUGETLB> or
+C<IO::AIO::MAP_STACK>.
 If C<$fh> is C<undef>, then a file descriptor of C<-1> is passed.
 C<$offset> is the offset from the start of the file - it generally must be
 a multiple of C<IO::AIO::PAGESIZE> and defaults to C<0>.
 See the C<splice(2)> manpage for details.
 =item IO::AIO::tee $r_fh, $w_fh, $length, $flags
-Calls the GNU/Linux C<tee(2)> syscall, see it's manpage and the
+Calls the GNU/Linux C<tee(2)> syscall, see its manpage and the
 description for C<IO::AIO::splice> above for details.
+=item $actual_size = IO::AIO::pipesize $r_fh[, $new_size]
+Attempts to query or change the pipe buffer size. Obviously works only
+on pipes, and currently works only on GNU/Linux systems, and fails with
+C<-1>/C<ENOSYS> everywhere else. If anybody knows how to influence pipe buffer
+size on other systems, drop me a note.
+=item ($rfh, $wfh) = IO::AIO::pipe2 [$flags]
+This is a direct interface to the Linux L<pipe2(2)> system call. If
+C<$flags> is missing or C<0>, then this should be the same as a call to
+perl's built-in C<pipe> function and create a new pipe, and works on
+systems that lack the pipe2 syscall. On win32, this case invokes C<_pipe
+(..., 4096, O_BINARY)>.
+If C<$flags> is non-zero, it tries to invoke the pipe2 system call with
+the given flags (Linux 2.6.27, glibc 2.9).
+On success, the read and write file handles are returned.
+On error, nothing will be returned. If the pipe2 syscall is missing and
+C<$flags> is non-zero, fails with C<ENOSYS>.
+Please refer to L<pipe2(2)> for more info on the C<$flags>, but at the
+time of this writing, C<IO::AIO::O_CLOEXEC>, C<IO::AIO::O_NONBLOCK> and
+C<IO::AIO::O_DIRECT> (Linux 3.4, for packet-based pipes) were supported.
+Example: create a pipe race-free w.r.t. threads and fork:
+   my ($rfh, $wfh) = IO::AIO::pipe2 IO::AIO::O_CLOEXEC
+      or die "pipe2: $!\n";
+=item $fh = IO::AIO::eventfd [$initval, [$flags]]
+This is a direct interface to the Linux L<eventfd(2)> system call. The
+(unhelpful) defaults for C<$initval> and C<$flags> are C<0> for both.
+On success, the new eventfd filehandle is returned, otherwise returns
+C<undef>. If the eventfd syscall is missing, fails with C<ENOSYS>.
+Please refer to L<eventfd(2)> for more info on this call.
+The following symbol flag values are available: C<IO::AIO::EFD_CLOEXEC>,
+C<IO::AIO::EFD_NONBLOCK> and C<IO::AIO::EFD_SEMAPHORE> (Linux 2.6.30).
+Example: create a new eventfd filehandle:
+   $fh = IO::AIO::eventfd 0, IO::AIO::O_CLOEXEC
+      or die "eventfd: $!\n";
+=item $fh = IO::AIO::timerfd_create $clockid[, $flags]
+This is a direct interface to the Linux L<timerfd_create(2)> system call. The
+(unhelpful) default for C<$flags> is C<0>.
+On success, the new timerfd filehandle is returned, otherwise returns
+C<undef>. If the eventfd syscall is missing, fails with C<ENOSYS>.
+Please refer to L<timerfd_create(2)> for more info on this call.
+The following C<$clockid> values are
+available: C<IO::AIO::CLOCK_REALTIME>, C<IO::AIO::CLOCK_MONOTONIC>
+C<IO::AIO::CLOCK_CLOCK_BOOTTIME> (Linux 3.15)
+C<IO::AIO::CLOCK_CLOCK_REALTIME_ALARM> (Linux 3.11) and
+C<IO::AIO::CLOCK_CLOCK_BOOTTIME_ALARM> (Linux 3.11).
+The following C<$flags> values are available (Linux
+2.6.27): C<IO::AIO::TFD_NONBLOCK> and C<IO::AIO::TFD_CLOEXEC>.
+Example: create a new timerfd and set it to one-second repeated alarms,
+then wait for two alarms:
+   my $fh = IO::AIO::timerfd_create IO::AIO::CLOCK_BOOTTIME, IO::AIO::TFD_CLOEXEC
+      or die "timerfd_create: $!\n";
+   defined IO::AIO::timerfd_settime $fh, 0, 1, 1
+      or die "timerfd_settime: $!\n";
+   for (1..2) {
+      8 == sysread $fh, my $buf, 8
+         or die "timerfd read failure\n";
+      printf "number of expirations (likely 1): %d\n",
+         unpack "Q", $buf;
+   }
+=item ($cur_interval, $cur_value) = IO::AIO::timerfd_settime $fh, $flags, $new_interval, $nbw_value
+This is a direct interface to the Linux L<timerfd_settime(2)> system
+call. Please refer to its manpage for more info on this call.
+The new itimerspec is specified using two (possibly fractional) second
+values, C<$new_interval> and C<$new_value>).
+On success, the current interval and value are returned (as per
+C<timerfd_gettime>). On failure, the empty list is returned.
+The following C<$flags> values are
+available: C<IO::AIO::TFD_TIMER_ABSTIME> and
+C<IO::AIO::TFD_TIMER_CANCEL_ON_SET>.
+See C<IO::AIO::timerfd_create> for a full example.
+=item ($cur_interval, $cur_value) = IO::AIO::timerfd_gettime $fh
+This is a direct interface to the Linux L<timerfd_gettime(2)> system
+call. Please refer to its manpage for more info on this call.
+On success, returns the current values of interval and value for the given
+timerfd (as potentially fractional second values). On failure, the empty
+list is returned.
 =back
 =cut
 the process will result in undefined behaviour. Calling it at any time
 will also result in any undefined (by POSIX) behaviour.
 =back
+=head2 LINUX-SPECIFIC CALLS
+When a call is documented as "linux-specific" then this means it
+originated on GNU/Linux. C<IO::AIO> will usually try to autodetect the
+availability and compatibility of such calls regardless of the platform
+it is compiled on, so platforms such as FreeBSD which often implement
+these calls will work. When in doubt, call them and see if they fail wth
+C<ENOSYS>.
 =head2 MEMORY USAGE
 Per-request usage:
 Each aio request uses - depending on your architecture - around 100-200

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Revision 1.282 by root, Tue Feb 20 05:23:47 2018 UTC