From 717da4b3bead186d8790b260d5c0dd317a651d8b Mon Sep 17 00:00:00 2001 From: Adhemerval Zanella Date: Mon, 1 May 2017 16:38:56 -0300 Subject: [PATCH] manual: Add preadv and pwritev documentation * manual/llio.texi: Add preadv and pwritev documentation. --- ChangeLog | 4 +++ manual/llio.texi | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 106 insertions(+) diff --git a/ChangeLog b/ChangeLog index a37bdd5..ee121d7 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,7 @@ +2017-05-04 Adhemerval Zanella + + * manual/llio.texi: Add preadv and pwritev documentation. + 2017-05-04 Joseph Myers [BZ #21455] diff --git a/manual/llio.texi b/manual/llio.texi index 9643bcb..9fad8f4 100644 --- a/manual/llio.texi +++ b/manual/llio.texi @@ -620,6 +620,10 @@ is not written to the current position of the file descriptor position @var{offset}. The position of the file descriptor itself is not affected by the operation. The value is the same as before the call. +However, on Linux, if a file is opened with @code{O_APPEND}, @code{pwrite} +appends data to the end of the file, regardless of the value of +@code{offset}. + When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the @code{pwrite} function is in fact @code{pwrite64} and the type @code{off_t} has 64 bits, which makes it possible to handle files up to @@ -662,6 +666,104 @@ When the source file is compiled using @code{_FILE_OFFSET_BITS == 64} on a @code{pwrite} and so transparently replaces the 32 bit interface. @end deftypefun +@comment sys/uio.h +@comment BSD +@deftypefun ssize_t preadv (int @var{fd}, const struct iovec *@var{iov}, int @var{iovcnt}, off_t @var{offset}) +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +@c This is a syscall for Linux 3.2 for all architectures but microblaze +@c (which was added on 3.15). The sysdeps/posix fallback emulation +@c is also MT-Safe since it calls pread, and it is now a syscall on all +@c targets. + +This function is similar to the @code{readv} function, with the difference +it adds an extra @var{offset} parameter of type @code{off_t} similar to +@code{pread}. The data is written to the file starting at position +@var{offset}. The position of the file descriptor itself is not affected +by the operation. The value is the same as before the call. + +When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the +@code{preadv} function is in fact @code{preadv64} and the type +@code{off_t} has 64 bits, which makes it possible to handle files up to +@twoexp{63} bytes in length. + +The return value is a count of bytes (@emph{not} buffers) read, @math{0} +indicating end-of-file, or @math{-1} indicating an error. The possible +errors are the same as in @code{readv} and @code{pread}. +@end deftypefun + +@comment unistd.h +@comment BSD +@deftypefun ssize_t preadv64 (int @var{fd}, const struct iovec *@var{iov}, int @var{iovcnt}, off64_t @var{offset}) +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +@c This is a syscall for Linux 3.2 for all architectures but microblaze +@c (which was added on 3.15). The sysdeps/posix fallback emulation +@c is also MT-Safe since it calls pread64, and it is now a syscall on all +@c targets. + +This function is similar to the @code{preadv} function with the difference +is that the @var{offset} parameter is of type @code{off64_t} instead of +@code{off_t}. It makes it possible on 32 bit machines to address +files larger than @twoexp{31} bytes and up to @twoexp{63} bytes. The +file descriptor @code{filedes} must be opened using @code{open64} since +otherwise the large offsets possible with @code{off64_t} will lead to +errors with a descriptor in small file mode. + +When the source file is compiled using @code{_FILE_OFFSET_BITS == 64} on a +32 bit machine this function is actually available under the name +@code{preadv} and so transparently replaces the 32 bit interface. +@end deftypefun + +@comment sys/uio.h +@comment BSD +@deftypefun ssize_t pwritev (int @var{fd}, const struct iovec *@var{iov}, int @var{iovcnt}, off_t @var{offset}) +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +@c This is a syscall for Linux 3.2 for all architectures but microblaze +@c (which was added on 3.15). The sysdeps/posix fallback emulation +@c is also MT-Safe since it calls pwrite, and it is now a syscall on all +@c targets. + +This function is similar to the @code{writev} function, with the difference +it adds an extra @var{offset} parameter of type @code{off_t} similar to +@code{pwrite}. The data is written to the file starting at position +@var{offset}. The position of the file descriptor itself is not affected +by the operation. The value is the same as before the call. + +However, on Linux, if a file is opened with @code{O_APPEND}, @code{pwrite} +appends data to the end of the file, regardless of the value of +@code{offset}. + +When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the +@code{pwritev} function is in fact @code{pwritev64} and the type +@code{off_t} has 64 bits, which makes it possible to handle files up to +@twoexp{63} bytes in length. + +The return value is a count of bytes (@emph{not} buffers) written, @math{0} +indicating end-of-file, or @math{-1} indicating an error. The possible +errors are the same as in @code{writev} and @code{pwrite}. +@end deftypefun + +@comment unistd.h +@comment BSD +@deftypefun ssize_t pwritev64 (int @var{fd}, const struct iovec *@var{iov}, int @var{iovcnt}, off64_t @var{offset}) +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +@c This is a syscall for Linux 3.2 for all architectures but microblaze +@c (which was added on 3.15). The sysdeps/posix fallback emulation +@c is also MT-Safe since it calls pwrite64, and it is now a syscall on all +@c targets. + +This function is similar to the @code{pwritev} function with the difference +is that the @var{offset} parameter is of type @code{off64_t} instead of +@code{off_t}. It makes it possible on 32 bit machines to address +files larger than @twoexp{31} bytes and up to @twoexp{63} bytes. The +file descriptor @code{filedes} must be opened using @code{open64} since +otherwise the large offsets possible with @code{off64_t} will lead to +errors with a descriptor in small file mode. + +When the source file is compiled using @code{_FILE_OFFSET_BITS == 64} on a +32 bit machine this function is actually available under the name +@code{pwritev} and so transparently replaces the 32 bit interface. +@end deftypefun + @node File Position Primitive @section Setting the File Position of a Descriptor -- 2.7.4