Adding upstream version 4.22.0.upstream/4.22.0

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.\" Copyright (C) 2011 Christopher Yeoh <cyeoh@au1.ibm.com>
+.\" and Copyright (C) 2012 Mike Frysinger <vapier@gentoo.org>
+.\" and Copyright (C) 2012 Michael Kerrisk <mtk.man-pages@gmail.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" Commit fcf634098c00dd9cd247447368495f0b79be12d1
+.\"
+.TH process_vm_readv 2 2023-02-05 "Linux man-pages 6.03"
+.SH NAME
+process_vm_readv, process_vm_writev \-
+transfer data between process address spaces
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.B #include <sys/uio.h>
+.PP
+.BI "ssize_t process_vm_readv(pid_t " pid ,
+.BI "                       const struct iovec *" local_iov ,
+.BI "                       unsigned long " liovcnt ,
+.BI "                       const struct iovec *" remote_iov ,
+.BI "                       unsigned long " riovcnt ,
+.BI "                       unsigned long " flags ");"
+.BI "ssize_t process_vm_writev(pid_t " pid ,
+.BI "                       const struct iovec *" local_iov ,
+.BI "                       unsigned long " liovcnt ,
+.BI "                       const struct iovec *" remote_iov ,
+.BI "                       unsigned long " riovcnt ,
+.BI "                       unsigned long " flags ");"
+.fi
+.PP
+.RS -4
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.RE
+.PP
+.BR process_vm_readv (),
+.BR process_vm_writev ():
+.nf
+    _GNU_SOURCE
+.fi
+.SH DESCRIPTION
+These system calls transfer data between the address space
+of the calling process ("the local process") and the process identified by
+.I pid
+("the remote process").
+The data moves directly between the address spaces of the two processes,
+without passing through kernel space.
+.PP
+The
+.BR process_vm_readv ()
+system call transfers data from the remote process to the local process.
+The data to be transferred is identified by
+.I remote_iov
+and
+.IR riovcnt :
+.I remote_iov
+is a pointer to an array describing address ranges in the process
+.IR pid ,
+and
+.I riovcnt
+specifies the number of elements in
+.IR remote_iov .
+The data is transferred to the locations specified by
+.I local_iov
+and
+.IR liovcnt :
+.I local_iov
+is a pointer to an array describing address ranges in the calling process,
+and
+.I liovcnt
+specifies the number of elements in
+.IR local_iov .
+.PP
+The
+.BR process_vm_writev ()
+system call is the converse of
+.BR process_vm_readv ()\[em]it
+transfers data from the local process to the remote process.
+Other than the direction of the transfer, the arguments
+.IR liovcnt ,
+.IR local_iov ,
+.IR riovcnt ,
+and
+.I remote_iov
+have the same meaning as for
+.BR process_vm_readv ().
+.PP
+The
+.I local_iov
+and
+.I remote_iov
+arguments point to an array of
+.I iovec
+structures, described in
+.BR iovec (3type).
+.PP
+Buffers are processed in array order.
+This means that
+.BR process_vm_readv ()
+completely fills
+.I local_iov[0]
+before proceeding to
+.IR local_iov[1] ,
+and so on.
+Likewise,
+.I remote_iov[0]
+is completely read before proceeding to
+.IR remote_iov[1] ,
+and so on.
+.PP
+Similarly,
+.BR process_vm_writev ()
+writes out the entire contents of
+.I local_iov[0]
+before proceeding to
+.IR local_iov[1] ,
+and it completely fills
+.I remote_iov[0]
+before proceeding to
+.IR remote_iov[1] .
+.PP
+The lengths of
+.I remote_iov[i].iov_len
+and
+.I local_iov[i].iov_len
+do not have to be the same.
+Thus, it is possible to split a single local buffer
+into multiple remote buffers, or vice versa.
+.PP
+The
+.I flags
+argument is currently unused and must be set to 0.
+.PP
+The values specified in the
+.I liovcnt
+and
+.I riovcnt
+arguments must be less than or equal to
+.B IOV_MAX
+(defined in
+.I <limits.h>
+or accessible via the call
+.IR sysconf(_SC_IOV_MAX) ).
+.\" In time, glibc might provide a wrapper that works around this limit,
+.\" as is done for readv()/writev()
+.PP
+The count arguments and
+.I local_iov
+are checked before doing any transfers.
+If the counts are too big, or
+.I local_iov
+is invalid,
+or the addresses refer to regions that are inaccessible to the local process,
+none of the vectors will be processed
+and an error will be returned immediately.
+.PP
+Note, however, that these system calls do not check the memory regions
+in the remote process until just before doing the read/write.
+Consequently, a partial read/write (see RETURN VALUE)
+may result if one of the
+.I remote_iov
+elements points to an invalid memory region in the remote process.
+No further reads/writes will be attempted beyond that point.
+Keep this in mind when attempting to read data of unknown length
+(such as C strings that are null-terminated) from a remote process,
+by avoiding spanning memory pages (typically 4\ KiB) in a single remote
+.I iovec
+element.
+(Instead, split the remote read into two
+.I remote_iov
+elements and have them merge back into a single write
+.I local_iov
+entry.
+The first read entry goes up to the page boundary,
+while the second starts on the next page boundary.)
+.PP
+Permission to read from or write to another process
+is governed by a ptrace access mode
+.B PTRACE_MODE_ATTACH_REALCREDS
+check; see
+.BR ptrace (2).
+.SH RETURN VALUE
+On success,
+.BR process_vm_readv ()
+returns the number of bytes read and
+.BR process_vm_writev ()
+returns the number of bytes written.
+This return value may be less than the total number of requested bytes,
+if a partial read/write occurred.
+(Partial transfers apply at the granularity of
+.I iovec
+elements.
+These system calls won't perform a partial transfer that splits a single
+.I iovec
+element.)
+The caller should check the return value to determine whether
+a partial read/write occurred.
+.PP
+On error, \-1 is returned and
+.I errno
+is set to indicate the error.
+.SH ERRORS
+.TP
+.B EFAULT
+The memory described by
+.I local_iov
+is outside the caller's accessible address space.
+.TP
+.B EFAULT
+The memory described by
+.I remote_iov
+is outside the accessible address space of the process
+.IR pid .
+.TP
+.B EINVAL
+The sum of the
+.I iov_len
+values of either
+.I local_iov
+or
+.I remote_iov
+overflows a
+.I ssize_t
+value.
+.TP
+.B EINVAL
+.I flags
+is not 0.
+.TP
+.B EINVAL
+.I liovcnt
+or
+.I riovcnt
+is too large.
+.TP
+.B ENOMEM
+Could not allocate memory for internal copies of the
+.I iovec
+structures.
+.TP
+.B EPERM
+The caller does not have permission to access the address space of the process
+.IR pid .
+.TP
+.B ESRCH
+No process with ID
+.I pid
+exists.
+.SH VERSIONS
+These system calls were added in Linux 3.2.
+Support is provided since glibc 2.15.
+.SH STANDARDS
+These system calls are nonstandard Linux extensions.
+.SH NOTES
+The data transfers performed by
+.BR process_vm_readv ()
+and
+.BR process_vm_writev ()
+are not guaranteed to be atomic in any way.
+.PP
+These system calls were designed to permit fast message passing
+by allowing messages to be exchanged with a single copy operation
+(rather than the double copy that would be required
+when using, for example, shared memory or pipes).
+.\" Original user is MPI, http://www.mcs.anl.gov/research/projects/mpi/
+.\" See also some benchmarks at http://lwn.net/Articles/405284/
+.\" and http://marc.info/?l=linux-mm&m=130105930902915&w=2
+.SH EXAMPLES
+The following code sample demonstrates the use of
+.BR process_vm_readv ().
+It reads 20 bytes at the address 0x10000 from the process with PID 10
+and writes the first 10 bytes into
+.I buf1
+and the second 10 bytes into
+.IR buf2 .
+.PP
+.\" SRC BEGIN (process_vm_readv.c)
+.EX
+#define _GNU_SOURCE
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+
+int
+main(void)
+{
+    char          buf1[10];
+    char          buf2[10];
+    pid_t         pid = 10;    /* PID of remote process */
+    ssize_t       nread;
+    struct iovec  local[2];
+    struct iovec  remote[1];
+
+    local[0].iov_base = buf1;
+    local[0].iov_len = 10;
+    local[1].iov_base = buf2;
+    local[1].iov_len = 10;
+    remote[0].iov_base = (void *) 0x10000;
+    remote[0].iov_len = 20;
+
+    nread = process_vm_readv(pid, local, 2, remote, 1, 0);
+    if (nread != 20)
+        exit(EXIT_FAILURE);
+
+    exit(EXIT_SUCCESS);
+}
+.EE
+.\" SRC END
+.SH SEE ALSO
+.BR readv (2),
+.BR writev (2)