plucky (2) process_madvise.2.gz

NAME

       process_madvise - give advice about use of memory to a process

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sys/mman.h>

       ssize_t process_madvise(int pidfd, const struct iovec iovec[.n],
                               size_t n, int advice, unsigned int flags);

DESCRIPTION

       The  process_madvise()  system  call is used to give advice or directions to the kernel about the address
       ranges of another process or of the calling process.  It provides  the  advice  for  the  address  ranges
       described by iovec and n.  The goal of such advice is to improve system or application performance.

       The  pidfd  argument is a PID file descriptor (see pidfd_open(2)) that specifies the process to which the
       advice is to be applied.

       The pointer iovec points to an array of iovec structures, described in iovec(3type).

       n specifies the number of elements in the array of iovec structures.  This value must  be  less  than  or
       equal to IOV_MAX (defined in <limits.h> or accessible via the call sysconf(_SC_IOV_MAX)).

       The advice argument is one of the following values:

       MADV_COLD
              See madvise(2).

       MADV_COLLAPSE
              See madvise(2).

       MADV_PAGEOUT
              See madvise(2).

       MADV_WILLNEED
              See madvise(2).

       The flags argument is reserved for future use; currently, this argument must be specified as 0.

       The  n and iovec arguments are checked before applying any advice.  If n is too big, or iovec is invalid,
       then an error will be returned immediately and no advice will be applied.

       The advice might be applied to only a part of iovec if one of its elements points to  an  invalid  memory
       region  in  the  remote  process.   No  further  elements  will be processed beyond that point.  (See the
       discussion regarding partial advice in RETURN VALUE.)

       Starting in Linux 5.12, permission to apply advice to another process is governed by ptrace  access  mode
       PTRACE_MODE_READ_FSCREDS  check  (see ptrace(2)); in addition, because of the performance implications of
       applying the advice, the caller must have the CAP_SYS_NICE capability (see capabilities(7)).

RETURN VALUE

       On success, process_madvise() returns the number of bytes advised.  This return value may  be  less  than
       the  total  number  of  requested  bytes,  if  an  error  occurred after some iovec elements were already
       processed.  The caller should check the return value to determine whether a partial advice occurred.

       On error, -1 is returned and errno is set to indicate the error.

ERRORS

       EBADF  pidfd is not a valid PID file descriptor.

       EFAULT The memory described by iovec is outside the accessible address space of the process  referred  to
              by pidfd.

       EINVAL flags is not 0.

       EINVAL The sum of the iov_len values of iovec overflows a ssize_t value.

       EINVAL n is too large.

       ENOMEM Could not allocate memory for internal copies of the iovec structures.

       EPERM  The caller does not have permission to access the address space of the process pidfd.

       ESRCH  The target process does not exist (i.e., it has terminated and been waited on).

       See madvise(2) for advice-specific errors.

STANDARDS

       Linux.

HISTORY

       Linux 5.10.  glibc 2.36.

       Support  for  this  system  call  is  optional,  depending  on  the setting of the CONFIG_ADVISE_SYSCALLS
       configuration option.

       When this system call first appeared in Linux 5.10, permission to apply advice  to  another  process  was
       entirely  governed  by  ptrace  access  mode  PTRACE_MODE_ATTACH_FSCREDS  check  (see  ptrace(2)).   This
       requirement was relaxed in Linux 5.12 so that the caller didn't require  full  control  over  the  target
       process.

SEE ALSO

       madvise(2), pidfd_open(2), process_vm_readv(2), process_vm_write(2)