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Update.
* manual/sysinfo.texi: Document fstab and mtab handling functions. * manual/llio.texi: Document more LFS functions and start documenting the AIO functions.
This commit is contained in:
Ulrich Drepper
parent
37742e84b2
commit
b07d03e000
@ -2,7 +2,9 @@
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* libc.map: Don't export argp's fmtstream handling functions.
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* manual/sysinfo.h: Document fstab and mtab handling functions.
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* manual/sysinfo.texi: Document fstab and mtab handling functions.
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* manual/llio.texi: Document more LFS functions and start documenting
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the AIO functions.
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1998-06-03 03:09 Geoff Keating <geoffk@ozemail.com.au>
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359
manual/llio.texi
359
manual/llio.texi
@ -43,6 +43,7 @@ directly.)
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* Waiting for I/O:: How to check for input or output
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on multiple file descriptors.
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* Synchronizing I/O:: Making sure all I/O actions completed.
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* Asynchronous I/O:: Perform I/O in parallel.
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* Control Operations:: Various other operations on file
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descriptors.
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* Duplicating Descriptors:: Fcntl commands for duplicating
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@ -138,6 +139,13 @@ or @code{O_CREAT} is set and the file does not already exist.
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@c !!! umask
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If on a 32 bits machine the sources are translated with
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@code{_FILE_OFFSET_BITS == 64} the function @code{open} returns a file
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descriptor opened in the large file mode which enables the file handling
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functions to use files up to @math{2^63} in size and offset from
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@math{-2^63} to @math{2^63}. This happens transparently for the user
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since all of the lowlevel file handling functions are equally replaced.
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This function is a cancelation point in multi-threaded programs. This
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is a problem if the thread allocates some resources (like memory, file
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descriptors, semaphores or whatever) at the time @code{open} is
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@ -150,6 +158,23 @@ The @code{open} function is the underlying primitive for the @code{fopen}
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and @code{freopen} functions, that create streams.
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@end deftypefun
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@comment fcntl.h
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@comment LFS
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@deftypefun int open64 (const char *@var{filename}, int @var{flags}[, mode_t @var{mode}])
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This function is similar to @code{open}. It returns a file descriptor
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which can be used to access the file named by @var{filename}. The only
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the difference is that on 32 bits systems the file is opened in the
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large file mode. I.e., file length and file offsets can exceed 31 bits.
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To use this file descriptor one must not use the normal operations but
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instead the counterparts named @code{*64}, e.g., @code{read64}.
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When the sources are translated with @code{_FILE_OFFSET_BITS == 64} this
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function is actually available under the name @code{open}. I.e., the
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new, extended API using 64 bit file sizes and offsets transparently
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replaces the old API.
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@end deftypefun
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@comment fcntl.h
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@comment POSIX.1
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@deftypefn {Obsolete function} int creat (const char *@var{filename}, mode_t @var{mode})
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@ -165,6 +190,30 @@ is equivalent to:
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@smallexample
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open (@var{filename}, O_WRONLY | O_CREAT | O_TRUNC, @var{mode})
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@end smallexample
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If on a 32 bits machine the sources are translated with
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@code{_FILE_OFFSET_BITS == 64} the function @code{creat} returns a file
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descriptor opened in the large file mode which enables the file handling
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functions to use files up to @math{2^63} in size and offset from
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@math{-2^63} to @math{2^63}. This happens transparently for the user
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since all of the lowlevel file handling functions are equally replaced.
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@end deftypefn
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@comment fcntl.h
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@comment LFS
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@deftypefn {Obsolete function} int creat64 (const char *@var{filename}, mode_t @var{mode})
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This function is similar to @code{creat}. It returns a file descriptor
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which can be used to access the file named by @var{filename}. The only
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the difference is that on 32 bits systems the file is opened in the
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large file mode. I.e., file length and file offsets can exceed 31 bits.
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To use this file descriptor one must not use the normal operations but
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instead the counterparts named @code{*64}, e.g., @code{read64}.
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When the sources are translated with @code{_FILE_OFFSET_BITS == 64} this
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function is actually available under the name @code{open}. I.e., the
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new, extended API using 64 bit file sizes and offsets transparently
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replaces the old API.
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@end deftypefn
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@comment unistd.h
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@ -217,6 +266,12 @@ When the file is accessed by NFS, these errors from @code{write} can sometimes
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not be detected until @code{close}. @xref{I/O Primitives}, for details
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on their meaning.
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@end table
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Please note that there is @emph{no} separate @code{close64} function.
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This is not necessary since this function does not determine nor depend
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on the more of the file. The kernel which performs the @code{close}
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operation knows for which mode the descriptor is used and can handle
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this situation.
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@end deftypefun
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To close a stream, call @code{fclose} (@pxref{Closing Streams}) instead
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@ -235,13 +290,18 @@ function. The prototypes for these functions are in @file{unistd.h}.
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@comment unistd.h
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@comment X/Open
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@deftypefun int truncate (const char *@var{name}, size_t @var{length})
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@deftypefun int truncate (const char *@var{name}, off_t @var{length})
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The @code{truncation} function truncates the file named by @var{name} to
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at most @var{length} bytes. I.e., if the file was larger before the
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extra bytes are stripped of. If the file was small or equal to
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@var{length} in size before nothing is done. The file must be writable
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by the user to perform this operation.
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When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
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@code{truncate} function is in fact @code{truncate64} and the type
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@code{off_t} has 64 bits which makes it possible to handle files up to
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@math{2^63} bytes.
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The return value is zero is everything went ok. Otherwise the return
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value is @math{-1} and the global variable @var{errno} is set to:
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@table @code
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@ -262,9 +322,22 @@ This function was introduced in 4.2BSD but also was available in later
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it is only of marginally additional utility. See below.
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@end deftypefun
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@comment unistd.h
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@comment LFS
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@deftypefun int truncate64 (const char *@var{name}, off64_t @var{length})
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This function is similar to the @code{truncate} function. The
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difference is that the @var{length} argument is even on 32 bits machines
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64 bits wide which allows to handle file with a size up to @math{2^63}
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bytes.
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When the sources are defined using @code{_FILE_OFFSET_BITS == 64} on a
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32 bits machine this function is actually available under the name
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@code{truncate} and so transparently replaces the 32 bits interface.
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@end deftypefun
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@comment unistd.h
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@comment POSIX
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@deftypefun int ftruncate (int @var{fd}, size_t @var{length})
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@deftypefun int ftruncate (int @var{fd}, off_t @var{length})
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The @code{ftruncate} function is similar to the @code{truncate}
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function. The main difference is that it takes a descriptor for an
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opened file instead of a file name to identify the object. The file
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@ -279,6 +352,11 @@ is no reliable way to increase the file size but if it is possible it is
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probably the fastest way. The function also operates on POSIX shared
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memory segments if these are implemented by the system.
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When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
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@code{ftruncate} function is in fact @code{ftruncate64} and the type
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@code{off_t} has 64 bits which makes it possible to handle files up to
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@math{2^63} bytes.
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On success the function returns zero. Otherwise it returns @math{-1}
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and set @var{errno} to one of these values:
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@table @code
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@ -291,6 +369,19 @@ The file is on a read-only file system.
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@end table
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@end deftypefun
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@comment unistd.h
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@comment LFS
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@deftypefun int ftruncate64 (int @var{id}, off64_t @var{length})
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This function is similar to the @code{ftruncate} function. The
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difference is that the @var{length} argument is even on 32 bits machines
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64 bits wide which allows to handle file with a size up to @math{2^63}
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bytes.
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When the sources are defined using @code{_FILE_OFFSET_BITS == 64} on a
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32 bits machine this function is actually available under the name
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@code{ftruncate} and so transparently replaces the 32 bits interface.
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@end deftypefun
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@node I/O Primitives
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@section Input and Output Primitives
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@ -382,6 +473,11 @@ orphaned. @xref{Job Control}, for more information about job control,
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and @ref{Signal Handling}, for information about signals.
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@end table
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Please note that there is no function named @code{read64}. This is not
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necessary since this function does not directly modify or handle the
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possibly wide file offset. Since the kernel handles this state
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internally the @code{read} function can be used for all cases.
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This function is a cancelation point in multi-threaded programs. This
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is a problem if the thread allocates some resources (like memory, file
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descriptors, semaphores or whatever) at the time @code{read} is
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@ -407,6 +503,11 @@ is not read from the current position of the file descriptor
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position @var{offset}. The position of the file descriptor itself is
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not effected by the operation. The value is the same as before the call.
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When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
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@code{pread} function is in fact @code{pread64} and the type
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@code{off_t} has 64 bits which makes it possible to handle files up to
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@math{2^63} bytes.
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The return value of @code{pread} describes the number of bytes read.
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In the error case it returns @math{-1} like @code{read} does and the
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error codes are also the same. Only there are a few more error codes:
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@ -423,6 +524,22 @@ The function is an extension defined in the Unix Single Specification
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version 2.
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@end deftypefun
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@comment unistd.h
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@comment LFS
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@deftypefun ssize_t pread64 (int @var{filedes}, void *@var{buffer}, size_t @var{size}, off64_t @var{offset})
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This function is similar to the @code{pread} function. The difference
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is that the @var{offset} parameter is of type @code{off64_t} instead of
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@code{off_t} which makes it possible on 32 bits machines to address
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files larger then @math{2^31} bytes and up to @math{2^63} bytes. The
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file descriptor @code{filedes} must be opened using @code{open64} since
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otherwise the large offsets possible with @code{off64_t} will lead to
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errors with a descriptor in small file mode.
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When the sources are defined using @code{_FILE_OFFSET_BITS == 64} on a
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32 bits machine this function is actually available under the name
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@code{pread} and so transparently replaces the 32 bits interface.
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@end deftypefun
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@cindex writing to a file descriptor
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@comment unistd.h
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@comment POSIX.1
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@ -512,6 +629,11 @@ macro @code{TEMP_FAILURE_RETRY}, as follows:
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nbytes = TEMP_FAILURE_RETRY (write (desc, buffer, count));
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@end smallexample
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Please note that there is no function named @code{write64}. This is not
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necessary since this function does not directly modify or handle the
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possibly wide file offset. Since the kernel handles this state
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internally the @code{write} function can be used for all cases.
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This function is a cancelation point in multi-threaded programs. This
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is a problem if the thread allocates some resources (like memory, file
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descriptors, semaphores or whatever) at the time @code{write} is
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@ -537,6 +659,11 @@ is not written to the current position of the file descriptor
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position @var{offset}. The position of the file descriptor itself is
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not effected by the operation. The value is the same as before the call.
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When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
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@code{pwrite} function is in fact @code{pwrite64} and the type
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@code{off_t} has 64 bits which makes it possible to handle files up to
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@math{2^63} bytes.
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The return value of @code{pwrite} describes the number of written bytes.
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In the error case it returns @math{-1} like @code{write} does and the
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error codes are also the same. Only there are a few more error codes:
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@ -553,6 +680,22 @@ The function is an extension defined in the Unix Single Specification
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version 2.
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@end deftypefun
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@comment unistd.h
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@comment LFS
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@deftypefun ssize_t pwrite64 (int @var{filedes}, const void *@var{buffer}, size_t @var{size}, off64_t @var{offset})
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This function is similar to the @code{pwrite} function. The difference
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is that the @var{offset} parameter is of type @code{off64_t} instead of
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@code{off_t} which makes it possible on 32 bits machines to address
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files larger then @math{2^31} bytes and up to @math{2^63} bytes. The
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file descriptor @code{filedes} must be opened using @code{open64} since
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otherwise the large offsets possible with @code{off64_t} will lead to
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errors with a descriptor in small file mode.
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When the sources are defined using @code{_FILE_OFFSET_BITS == 64} on a
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32 bits machine this function is actually available under the name
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@code{pwrite} and so transparently replaces the 32 bits interface.
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@end deftypefun
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@node File Position Primitive
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@section Setting the File Position of a Descriptor
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@ -638,6 +781,11 @@ only for pipes and FIFOs, but in the GNU system, you always get
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@code{ESPIPE} if the object is not seekable.)
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@end table
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When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
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@code{lseek} function is in fact @code{lseek64} and the type
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@code{off_t} has 64 bits which makes it possible to handle files up to
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@math{2^63} bytes.
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This function is a cancelation point in multi-threaded programs. This
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is a problem if the thread allocates some resources (like memory, file
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descriptors, semaphores or whatever) at the time @code{lseek} is
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@ -652,6 +800,22 @@ The @code{lseek} function is the underlying primitive for the
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descriptors.
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@end deftypefun
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@comment unistd.h
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@comment LFS
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@deftypefun off64_t lseek64 (int @var{filedes}, off64_t @var{offset}, int @var{whence})
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This function is similar to the @code{lseek} function. The difference
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is that the @var{offset} parameter is of type @code{off64_t} instead of
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@code{off_t} which makes it possible on 32 bits machines to address
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files larger then @math{2^31} bytes and up to @math{2^63} bytes. The
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file descriptor @code{filedes} must be opened using @code{open64} since
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otherwise the large offsets possible with @code{off64_t} will lead to
|
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errors with a descriptor in small file mode.
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When the sources are defined using @code{_FILE_OFFSET_BITS == 64} on a
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32 bits machine this function is actually available under the name
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@code{lseek} and so transparently replaces the 32 bits interface.
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@end deftypefun
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You can have multiple descriptors for the same file if you open the file
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more than once, or if you duplicate a descriptor with @code{dup}.
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Descriptors that come from separate calls to @code{open} have independent
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@ -706,6 +870,15 @@ This is an arithmetic data type used to represent file sizes.
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In the GNU system, this is equivalent to @code{fpos_t} or @code{long int}.
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@end deftp
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@comment sys/types.h
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@comment LFS
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@deftp {Data Type} off64_t
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This type is used similar to @code{off_t}. The difference is that even
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on 32 bits machines, where the @code{off_t} type would 32 bits,
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@code{off64_t} has 64 bits and so is able to address files up to
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@math{2^63} bytes in length.
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@end deftp
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These aliases for the @samp{SEEK_@dots{}} constants exist for the sake
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of compatibility with older BSD systems. They are defined in two
|
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different header files: @file{fcntl.h} and @file{sys/file.h}.
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@ -1211,6 +1384,188 @@ No synchronization is possible since the system does not implement this.
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@end deftypefun
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@node Asynchronous I/O
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@section Perform I/O Operations in Parallel
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|
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The POSIX.1b standard defines a new set of I/O operations which can
|
||||
reduce the time an application spends waiting at I/O significantly. The
|
||||
new functions allow a program to initiate one or more I/O operations and
|
||||
then immediately resume the normal word while the I/O operations are
|
||||
executed in parallel.
|
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|
||||
These functions are part of the library with realtime functions named
|
||||
@file{librt}. They are not actually part of the @file{libc} binary.
|
||||
The implementation of these functions can be done using support in the
|
||||
kernel )if available) or using a implementation based on threads at
|
||||
userlevel. In the later case it might be necessary to link applications
|
||||
linked with @file{librt} also with the thread library @file{libthread}.
|
||||
|
||||
All AIO operations operate on files which previously were opened. There
|
||||
might be arbitrary many operations for one file running. The
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||||
asynchronous I/O operations are controlled using a data structure named
|
||||
@code{struct aiocb} (@dfn{AIO control block}). It is defined in
|
||||
@file{aio.h} as follows.
|
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|
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@comment aio.h
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@comment POSIX.1b
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@deftp {Data Type} {struct aiocb}
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The POSIX.1b standard mandates that the @code{struct aiocb} structure
|
||||
contains at least the members described in the following table. There
|
||||
might be more elements which are used by the implementation but
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depending on these elements is not portable and is highly deprecated.
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@table @code
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@item int aio_fildes
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||||
This element specifies the file descriptor which is used for the
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operation. It must be a legal descriptor since otherwise the operation
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fails for obvious reasons.
|
||||
|
||||
The device on which the file is opened must allow the seek operation.
|
||||
I.e., it is not possible to use any of the AIO operations on devices
|
||||
like terminals where an @code{lseek} call would lead to an error.
|
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|
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@item off_t aio_offset
|
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This element specified at which offset in the file the operation (input
|
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or output) is performed. Since the operation are carried in arbitrary
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order and more than one operation for one file descriptor can be
|
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started, one cannot expect a current read/write position of the file
|
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descriptor.
|
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|
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@item volatile void *aio_buf
|
||||
This is a pointer to the buffer with the data to be written or the place
|
||||
where the ead data is stored.
|
||||
|
||||
@item size_t aio_nbytes
|
||||
This element specifies the length of the buffer pointed to by @code{aio_buf}.
|
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|
||||
@item int aio_reqprio
|
||||
If for the platform @code{_POSIX_PRIORITIZED_IO} and
|
||||
@code{_POSIX_PRIORITY_SCHEDULING} is defined the AIO requests are
|
||||
processed based on the current scheduling priority. The
|
||||
@code{aio_reqprio} element can then be used to lower the priority of the
|
||||
AIO operation.
|
||||
|
||||
@item struct sigevent aio_sigevent
|
||||
This element specifies how the calling process is notified once the
|
||||
operation terminated. If the @code{sigev_notify} element is
|
||||
@code{SIGEV_NONE} no notification is send. If it is @code{SIGEV_SIGNAL}
|
||||
the signal determined by @code{sigev_signo} is send. Otherwise
|
||||
@code{sigev_notify} must be @code{SIGEV_THREAD} in which case a thread
|
||||
which starts executing the function pointeed to by
|
||||
@code{sigev_notify_function}.
|
||||
|
||||
@item int aio_lio_opcode
|
||||
This element is only used by the @code{lio_listio} and
|
||||
@code{[lio_listio64} functions. Since these functions allow to start an
|
||||
arbitrary number of operations at once and since each operationcan be
|
||||
input or output (or nothing) the information must be stored in the
|
||||
control block. The possible values are:
|
||||
|
||||
@vtable @code
|
||||
@item LIO_READ
|
||||
Start a read operation. Read from the file at position
|
||||
@code{aio_offset} and store the next @code{aio_nbytes} bytes in the
|
||||
buffer pointed to by @code{aio_buf}.
|
||||
|
||||
@item LIO_WRITE
|
||||
Start a write operation. Write @code{aio_nbytes} bytes starting at
|
||||
@code{aio_buf} into the file starting at position @code{aio_offset}.
|
||||
|
||||
@item LIO_NOP
|
||||
Do nothing for this control block. This value is useful sometimes when
|
||||
an array of @code{struct aiocb} values contains holes, i.e., some of the
|
||||
values must not be handled allthough the whole array is presented to the
|
||||
@code{lio_listio} function.
|
||||
@end vtable
|
||||
@end table
|
||||
@end deftp
|
||||
|
||||
@menu
|
||||
* Asynchronous Reads:: Asynchronous Read Operations.
|
||||
* Cancel AIO Operations:: Cancelation of AIO Operations.
|
||||
@end menu
|
||||
|
||||
@node Asynchronous Reads
|
||||
@subsection Asynchronous Read Operations
|
||||
|
||||
@comment aio.h
|
||||
@comment POSIX.1b
|
||||
@deftypefun int aio_read (struct aiocb *@var{aiocbp})
|
||||
This function initiates an asynchronous read operation. The function
|
||||
call immedaitely returns after the operation was enqueued or if before
|
||||
this happens an error was encoutered.
|
||||
|
||||
The first @code{aiocbp->aio_nbytes} bytes from the buffer starting at
|
||||
@code{aiocbp->aio_buf} are written to the file for which
|
||||
@code{aiocbp->aio_fildes} is an descriptor, starting at the absolute
|
||||
position @code{aiocbp->aio_offset} in the file.
|
||||
|
||||
If prioritized I/O is supported by the platform the
|
||||
@code{aiocbp->aio_reqprio} value is used to adjust the priority before
|
||||
the request is actually enqueued.
|
||||
|
||||
The calling process is notified about the termination of the read
|
||||
request according to the @code{aiocbp->aio_sigevent} value.
|
||||
|
||||
When @code{aio_read} returns the return value is zero if no error
|
||||
occurred that can be found before the process is enqueued. If such an
|
||||
earlier error is found the function returns @code{-1} and sets
|
||||
@code{errno} to one of the following values.
|
||||
|
||||
@table @code
|
||||
@item EAGAIN
|
||||
The request was not enqueued due to (temporarily) exceeded resource
|
||||
limitations.
|
||||
@item ENOSYS
|
||||
The @code{aio_read} function is not implemented.
|
||||
@item EBADF
|
||||
The @code{aiocbp->aio_fildes} descriptor is not valid. This condition
|
||||
need not be recognized before enqueueing the request and so this error
|
||||
might also be signaled asynchrously.
|
||||
@item EINVAL
|
||||
The @code{aiocbp->aio_offset} or @code{aiocbp->aio_reqpiro} value is
|
||||
invalid. This condition need not be recognized before enqueueing the
|
||||
request and so this error might also be signaled asynchrously.
|
||||
@end table
|
||||
|
||||
In the case @code{aio_read} return zero the current status of the
|
||||
request can be queried using @code{aio_error} and @code{aio_return}
|
||||
questions. As long as the value returned by @code{aio_error} is
|
||||
@code{EINPROGRESS} the operation has not yet completed. If
|
||||
@code{aio_error} returns zero the operation successfully terminated,
|
||||
otherwise the value is to be interpreted as an error code. If the
|
||||
function terminated the result of the operation can be get using a call
|
||||
to @code{aio_return}. The returned value is the same as an equivalent
|
||||
call to @code{read} would have returned. Possible error code returned
|
||||
by @code{aio_error} are:
|
||||
|
||||
@table @code
|
||||
@item EBADF
|
||||
The @code{aiocbp->aio_fildes} descriptor is not valid.
|
||||
@item ECANCELED
|
||||
The operation was canceled before the operation was finished
|
||||
(@pxref{Cancel AIO Operations})
|
||||
@item EINVAL
|
||||
The @code{aiocbp->aio_offset} value is invalid.
|
||||
@end table
|
||||
@end deftypefun
|
||||
|
||||
@comment aio.h
|
||||
@comment POSIX.1b
|
||||
@deftypefun int aio_read64 (struct aiocb *@var{aiocbp})
|
||||
This function is similar to the @code{aio_read} function. The only
|
||||
difference is that only @w{32 bits} machines the file descriptor should
|
||||
be opened in the large file mode. Internally @code{aio_read64} uses
|
||||
functionality equivalent to @code{lseek64} to position the file
|
||||
descriptor correctly for the reading, as opposed to @code{lseek}
|
||||
funcationality used in @code{aio_read}.
|
||||
@end deftypefun
|
||||
|
||||
|
||||
@node Cancel AIO Operations
|
||||
@subsection Cancelation of AIO Operations
|
||||
|
||||
|
||||
@node Control Operations
|
||||
@section Control Operations on Files
|
||||
|
||||
|
||||
@ -481,7 +481,7 @@ This function takes for the @var{stream} parameter a file handle which
|
||||
previously was returned from the @code{setmntent} call.
|
||||
@code{endmntent} closes the stream and frees all resources.
|
||||
|
||||
The return value is @code[1} unless an error occurred in which case it
|
||||
The return value is @code{1} unless an error occurred in which case it
|
||||
is @code{0}.
|
||||
@end deftypefun
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user