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process_vm_readv.2: New page for process_vm_readv(2) and process_vm_writev(2)
Cowritten-by: Christopher Yeoh <cyeoh@au1.ibm.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Mike Frysinger
Michael Kerrisk
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.\" Copyright (C) 2011 Christopher Yeoh <cyeoh@au1.ibm.com>
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.\" Copyright (C) 2012 Mike Frysinger <vapier@gentoo.org>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH PROCESS_VM_READV 2 2012-03-09 "Linux" "Linux Programmer's Manual"
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.SH NAME
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process_vm_readv, process_vm_writev \- read/write from/to another processes' address space
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.SH SYNOPSIS
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.B #include <sys/uio.h>
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.sp
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.BI "ssize_t process_vm_readv(pid_t " pid ,
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.br
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.BI " const struct iovec *" lvec ,
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.br
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.BI " unsigned long " liovcnt ,
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.br
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.BI " const struct iovec *" rvec ,
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.br
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.BI " unsigned long " riovcnt ,
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.br
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.BI " unsigned long " flags ");"
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.BI "ssize_t process_vm_writev(pid_t " pid ,
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.br
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.BI " const struct iovec *" lvec ,
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.br
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.BI " unsigned long " liovcnt ,
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.br
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.BI " const struct iovec *" rvec ,
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.br
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.BI " unsigned long " riovcnt ,
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.br
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.BI " unsigned long " flags ");"
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.SH DESCRIPTION
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The
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.BR process_vm_readv ()
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function reads from the memory locations described by the \fIriovcnt\fP
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buffers from \fIrvec\fP in the process identified by \fIpid\fP into
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\fIliovcnt\fP buffers described by \fIlvec\fP in the current process.
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The
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.BR process_vm_writev ()
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function is the inverse of
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.BR process_vm_readv ()
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\-\- it writes into the memory locations described by \fIriovcnt\fP buffers
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from \fIrvec\fP in the process identified by \fIpid\fP into \fIliovcnt\fP
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buffers described by \fIlvec\fP in the current process.
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The count values might be individually capped according to \fIUIO_MAXIOV\fP.
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If the Linux kernel is capped at smaller values, the C library will take care
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of emulating the limit it exposes (if it is bigger) so the user only needs to
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care about that (what the C library defines).
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The pointers \fIlvec\fP and \fIrvec\fP point to an array of iovec structures
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defined in
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.IR <sys/uio.h>
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as:
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.in +4n
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.nf
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struct iovec {
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void *iov_base; /* Starting address */
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size_t iov_len; /* Number of bytes to transfer */
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};
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.fi
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.in
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Buffers are processed in array order. This means that
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.BR process_vm_readv ()
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completely fills \fIlvec[0]\fP before proceeding to \fIlvec[1]\fP, and
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so on. Along those lines, \fIrvec[0]\fP is completely read before
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proceeding to \fIrvec[1]\fP and so on.
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Similarly,
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.BR process_vm_writev ()
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writes out the entire contents of \fIlvec[0]\fP before proceeding to
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\fIlvec[1]\fP, and it completely fills \fIrevc[0]\fP before proceeding
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to \fIrvec[1]\fP.
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The lengths of \fIrvec[i]\fP and \fIlvec[i]\fP do not have to be the same.
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This allows you to split a single local buffer into multiple remote buffers,
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or vice versa.
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The data transfers of
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.BR process_vm_readv ()
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and
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.BR process_vm_writev ()
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are not guaranteed to be atomic in any way.
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The counts and vectors are checked before doing any transfers. So if the
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counts are too big, or the vectors invalid, or the addresses refer to regions
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that are inaccessible, none of the previous vectors will be processed and an
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error will be returned immediately. Keep this in mind when attempting to
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extract data of unknown length (such as C strings which are NULL terminated)
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by avoiding spanning memory pages (typically 4KiB).
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The \fIflags\fP parameter is currently unused and must be set to 0.
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In order to read or write from or to another process you must have
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the capability
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.BR CAP_SYS_PTRACE
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or have the same uid and gid of the target process. The permission
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required is exactly the same as being able to perform a
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.BR ptrace (2)
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ptrace with
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.BR PTRACE_ATTACH
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on the target process.
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.SH "RETURN VALUE"
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On success,
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.BR process_vm_readv ()
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returns the number of bytes read while
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.BR process_vm_writev ()
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returns the number of bytes written.
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On error, the number of bytes read or written is returned, or -1 is
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returned if it was unable to read/write any bytes; in either case,
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.I errno
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is set appropriately.
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.SH ERRORS
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.TP
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.B EINVAL
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The sum of the \fIiov_len\fP values of either \fIlvec\fP or \fIrvec\fP
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overflows a ssize_t value.
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.TP
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.B EINVAL
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The value of the \fIflags\fP parameter is not 0.
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.TP
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.B EFAULT
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The memory described by \fIlvec\fP is outside your accessible address space.
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.TP
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.B EFAULT
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The memory described by \fIrvec\fP is outside the accessible address space
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of process \fIpid\fP.
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.TP
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.B ENOMEM
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Out of memory.
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.TP
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.B EPERM
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.RB ( process_vm_readv ())
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You do not have permission to read from process \fIpid\fP.
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.TP
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.B EPERM
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.RB ( process_vm_writev ())
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You do not have permission to write to process \fIpid\fP.
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.TP
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.B ESRCH
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\fIpid\fP does not exist.
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.SH VERSIONS
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These functions are available since glibc 2.15 and Linux 3.2.
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.SH "CONFORMING TO"
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These functions are Linux extensions, not in C or POSIX.
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.SH EXAMPLE
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The following code sample demonstrates the use of process_vm_readv().
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It reads 20 bytes at the address 0x10000 from the process with PID 10
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and writes the first 10 bytes into buf1 and the second 10 bytes into
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buf2.
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.sp
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.nf
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#include <sys/uio.h>
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int main()
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{
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struct iovec local[2];
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struct iovec remote[1];
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char buf1[10];
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char buf2[10];
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ssize_t nread;
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pid_t pid = 10; /* PID of target process */
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local[0].iov_base = buf1;
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local[0].iov_len = 10;
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local[1].iov_base = buf2;
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local[1].iov_len = 10;
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remote[0].iov_base = (void *)0x10000;
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remote[1].iov_len = 20;
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nread = process_vm_readv(pid, local, 2, remote, 1, 0);
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if (nread != 20)
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return 1;
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else
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return 0;
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}
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.fi
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.SH "SEE ALSO"
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.BR readv (2),
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.BR writev (2)
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