- Add two new system calls: preadv() and pwritev() which are like readv()

  and writev() except that they take an additional offset argument and do
  not change the current file position.  In SAT speak:
  preadv:readv::pread:read and pwritev:writev::pwrite:write.
- Try to reduce code duplication some by merging most of the old
  kern_foov() and dofilefoo() functions into new dofilefoo() functions
  that are called by kern_foov() and kern_pfoov().  The non-v functions
  now all generate a simple uio on the stack from the passed in arguments
  and then call kern_foov().  For example, read() now just builds a uio and
  calls kern_readv() and pwrite() just builds a uio and calls kern_pwritev().

PR:		kern/80362
Submitted by:	Marc Olzheim marcolz at stack dot nl (1)
Approved by:	re (scottl)
MFC after:	1 week

1 files changed, 25 insertions, 8 deletions

diff --git a/lib/libc/sys/read.2 b/lib/libc/sys/read.2
index 8dd7731..fb452e9 100644
--- a/lib/libc/sys/read.2
+++ b/lib/libc/sys/read.2
@@ -38,7 +38,8 @@
 .Sh NAME
 .Nm read ,
 .Nm readv ,
-.Nm pread
+.Nm pread ,
+.Nm preadv
 .Nd read input
 .Sh LIBRARY
 .Lb libc
@@ -49,9 +50,11 @@
 .Ft ssize_t
 .Fn read "int d" "void *buf" "size_t nbytes"
 .Ft ssize_t
+.Fn pread "int d" "void *buf" "size_t nbytes" "off_t offset"
+.Ft ssize_t
 .Fn readv "int d" "const struct iovec *iov" "int iovcnt"
 .Ft ssize_t
-.Fn pread "int d" "void *buf" "size_t nbytes" "off_t offset"
+.Fn preadv "int d" "const struct iovec *iov" "int iovcnt" "off_t offset"
 .Sh DESCRIPTION
 The
 .Fn read
@@ -73,12 +76,16 @@ buffers specified by the members of the
 array: iov[0], iov[1], ..., iov[iovcnt\|\-\|1].
 The
 .Fn pread
-system call
-performs the same function, but reads from the specified position in
+and
+.Fn preadv
+system calls
+perform the same functions, but read from the specified position in
 the file without modifying the file pointer.
 .Pp
 For
-.Fn readv ,
+.Fn readv
+and
+.Fn preadv ,
 the
 .Fa iovec
 structure is defined as:
@@ -119,8 +126,9 @@ object is undefined.
 Upon successful completion,
 .Fn read ,
 .Fn readv ,
-and
 .Fn pread
+and
+.Fn preadv
 return the number of bytes actually read and placed in the buffer.
 The system guarantees to read the number of bytes requested if
 the descriptor references a normal file that has that many bytes left
@@ -137,8 +145,9 @@ is set to indicate the error.
 The
 .Fn read ,
 .Fn readv ,
-and
 .Fn pread
+and
+.Fn preadv
 system calls
 will succeed unless:
 .Bl -tag -width Er
@@ -189,6 +198,8 @@ is greater than
 .Pp
 In addition,
 .Fn readv
+and
+.Fn preadv
 may return one of the following errors:
 .Bl -tag -width Er
 .It Bq Er EINVAL
@@ -217,7 +228,9 @@ array points outside the process's allocated address space.
 .Pp
 The
 .Fn pread
-system call may also return the following errors:
+and
+.Fn preadv
+system calls may also return the following errors:
 .Bl -tag -width Er
 .It Bq Er EINVAL
 The
@@ -250,6 +263,10 @@ system calls are expected to conform to
 .St -xpg4.2 .
 .Sh HISTORY
 The
+.Fn preadv
+system call appeared in
+.Fx 6.0 .
+The
 .Fn pread
 function appeared in
 .At V.4 .