ps_status.c

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/*--------------------------------------------------------------------
 * ps_status.c
 *
 * Routines to support changing the ps display of PostgreSQL backends
 * to contain some useful information. Mechanism differs wildly across
 * platforms.
 *
 * src/backend/utils/misc/ps_status.c
 *
 * Copyright (c) 2000-2025, PostgreSQL Global Development Group
 * various details abducted from various places
 *--------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include <unistd.h>
#if defined(__darwin__)
#include <crt_externs.h>
#endif
 
#include "miscadmin.h"
#include "utils/guc.h"
#include "utils/ps_status.h"
 
#if !defined(WIN32) || defined(_MSC_VER)
extern char **environ;
#endif
 
/* GUC variable */
bool        update_process_title = DEFAULT_UPDATE_PROCESS_TITLE;
 
/*
 * Alternative ways of updating ps display:
 *
 * PS_USE_SETPROCTITLE_FAST
 *     use the function setproctitle_fast(const char *, ...)
 *     (FreeBSD)
 * PS_USE_SETPROCTITLE
 *     use the function setproctitle(const char *, ...)
 *     (other BSDs)
 * PS_USE_CLOBBER_ARGV
 *     write over the argv and environment area
 *     (Linux and most SysV-like systems)
 * PS_USE_WIN32
 *     push the string out as the name of a Windows event
 * PS_USE_NONE
 *     don't update ps display
 *     (This is the default, as it is safest.)
 */
#if defined(HAVE_SETPROCTITLE_FAST)
#define PS_USE_SETPROCTITLE_FAST
#elif defined(HAVE_SETPROCTITLE)
#define PS_USE_SETPROCTITLE
#elif defined(__linux__) || defined(__sun) || defined(__darwin__)
#define PS_USE_CLOBBER_ARGV
#elif defined(WIN32)
#define PS_USE_WIN32
#else
#define PS_USE_NONE
#endif
 
 
/* Different systems want the buffer padded differently */
#if defined(__linux__) || defined(__darwin__)
#define PS_PADDING '\0'
#else
#define PS_PADDING ' '
#endif
 
 
#ifndef PS_USE_NONE
 
#ifndef PS_USE_CLOBBER_ARGV
/* all but one option need a buffer to write their ps line in */
#define PS_BUFFER_SIZE 256
static char ps_buffer[PS_BUFFER_SIZE];
static const size_t ps_buffer_size = PS_BUFFER_SIZE;
#else                           /* PS_USE_CLOBBER_ARGV */
static char *ps_buffer;         /* will point to argv area */
static size_t ps_buffer_size;   /* space determined at run time */
static size_t last_status_len;  /* use to minimize length of clobber */
#endif                          /* PS_USE_CLOBBER_ARGV */
 
static size_t ps_buffer_cur_len;    /* nominal strlen(ps_buffer) */
 
static size_t ps_buffer_fixed_size; /* size of the constant prefix */
 
/*
 * Length of ps_buffer before the suffix was appended to the end, or 0 if we
 * didn't set a suffix.
 */
static size_t ps_buffer_nosuffix_len;
 
static void flush_ps_display(void);
 
#endif                          /* not PS_USE_NONE */
 
/* save the original argv[] location here */
static int  save_argc;
static char **save_argv;
 
/*
 * Valgrind seems not to consider the global "environ" variable as a valid
 * root pointer; so when we allocate a new environment array, it claims that
 * data is leaked.  To fix that, keep our own statically-allocated copy of the
 * pointer.  (Oddly, this doesn't seem to be a problem for "argv".)
 */
#if defined(PS_USE_CLOBBER_ARGV) && defined(USE_VALGRIND)
extern char **ps_status_new_environ;
char      **ps_status_new_environ;
#endif
 
 
/*
 * Call this early in startup to save the original argc/argv values.
 * If needed, we make a copy of the original argv[] array to preserve it
 * from being clobbered by subsequent ps_display actions.
 *
 * (The original argv[] will not be overwritten by this routine, but may be
 * overwritten during init_ps_display.  Also, the physical location of the
 * environment strings may be moved, so this should be called before any code
 * that might try to hang onto a getenv() result.  But see hack for musl
 * within.)
 *
 * Note that in case of failure this cannot call elog() as that is not
 * initialized yet.  We rely on write_stderr() instead.
 */
char      **
save_ps_display_args(int argc, char **argv)
{
    save_argc = argc;
    save_argv = argv;
 
#if defined(PS_USE_CLOBBER_ARGV)
 
    /*
     * If we're going to overwrite the argv area, count the available space.
     * Also move the environment strings to make additional room.
     */
    {
        char       *end_of_area = NULL;
        char      **new_environ;
        int         i;
 
        /*
         * check for contiguous argv strings
         */
        for (i = 0; i < argc; i++)
        {
            if (i == 0 || end_of_area + 1 == argv[i])
                end_of_area = argv[i] + strlen(argv[i]);
        }
 
        if (end_of_area == NULL)    /* probably can't happen? */
        {
            ps_buffer = NULL;
            ps_buffer_size = 0;
            return argv;
        }
 
        /*
         * check for contiguous environ strings following argv
         */
        for (i = 0; environ[i] != NULL; i++)
        {
            if (end_of_area + 1 == environ[i])
            {
                /*
                 * The musl dynamic linker keeps a static pointer to the
                 * initial value of LD_LIBRARY_PATH, if that is defined in the
                 * process's environment. Therefore, we must not overwrite the
                 * value of that setting and thus cannot advance end_of_area
                 * beyond it.  Musl does not define any identifying compiler
                 * symbol, so we have to do this unless we see a symbol
                 * identifying a Linux libc we know is safe.
                 */
#if defined(__linux__) && (!defined(__GLIBC__) && !defined(__UCLIBC__))
                if (strncmp(environ[i], "LD_LIBRARY_PATH=", 16) == 0)
                {
                    /*
                     * We can overwrite the name, but stop at the equals sign.
                     * Future loop iterations will not find any more
                     * contiguous space, but we don't break early because we
                     * need to count the total number of environ[] entries.
                     */
                    end_of_area = environ[i] + 15;
                }
                else
#endif
                {
                    end_of_area = environ[i] + strlen(environ[i]);
                }
            }
        }
 
        ps_buffer = argv[0];
        last_status_len = ps_buffer_size = end_of_area - argv[0];
 
        /*
         * move the environment out of the way
         */
        new_environ = (char **) malloc((i + 1) * sizeof(char *));
        if (!new_environ)
        {
            write_stderr("out of memory\n");
            exit(1);
        }
        for (i = 0; environ[i] != NULL; i++)
        {
            new_environ[i] = strdup(environ[i]);
            if (!new_environ[i])
            {
                write_stderr("out of memory\n");
                exit(1);
            }
        }
        new_environ[i] = NULL;
        environ = new_environ;
 
        /* See notes about Valgrind above. */
#ifdef USE_VALGRIND
        ps_status_new_environ = new_environ;
#endif
    }
 
    /*
     * If we're going to change the original argv[] then make a copy for
     * argument parsing purposes.
     *
     * NB: do NOT think to remove the copying of argv[], even though
     * postmaster.c finishes looking at argv[] long before we ever consider
     * changing the ps display.  On some platforms, getopt() keeps pointers
     * into the argv array, and will get horribly confused when it is
     * re-called to analyze a subprocess' argument string if the argv storage
     * has been clobbered meanwhile.  Other platforms have other dependencies
     * on argv[].
     */
    {
        char      **new_argv;
        int         i;
 
        new_argv = (char **) malloc((argc + 1) * sizeof(char *));
        if (!new_argv)
        {
            write_stderr("out of memory\n");
            exit(1);
        }
        for (i = 0; i < argc; i++)
        {
            new_argv[i] = strdup(argv[i]);
            if (!new_argv[i])
            {
                write_stderr("out of memory\n");
                exit(1);
            }
        }
        new_argv[argc] = NULL;
 
#if defined(__darwin__)
 
        /*
         * macOS has a static copy of the argv pointer, which we may fix like
         * so:
         */
        *_NSGetArgv() = new_argv;
#endif
 
        argv = new_argv;
    }
#endif                          /* PS_USE_CLOBBER_ARGV */
 
    return argv;
}
 
/*
 * Call this once during subprocess startup to set the identification
 * values.
 *
 * If fixed_part is NULL, a default will be obtained from MyBackendType.
 *
 * At this point, the original argv[] array may be overwritten.
 */
void
init_ps_display(const char *fixed_part)
{
#ifndef PS_USE_NONE
    bool        save_update_process_title;
#endif
 
    Assert(fixed_part || MyBackendType);
    if (!fixed_part)
        fixed_part = GetBackendTypeDesc(MyBackendType);
 
#ifndef PS_USE_NONE
    /* no ps display for stand-alone backend */
    if (!IsUnderPostmaster)
        return;
 
    /* no ps display if you didn't call save_ps_display_args() */
    if (!save_argv)
        return;
 
#ifdef PS_USE_CLOBBER_ARGV
    /* If ps_buffer is a pointer, it might still be null */
    if (!ps_buffer)
        return;
 
    /* make extra argv slots point at end_of_area (a NUL) */
    for (int i = 1; i < save_argc; i++)
        save_argv[i] = ps_buffer + ps_buffer_size;
#endif                          /* PS_USE_CLOBBER_ARGV */
 
    /*
     * Make fixed prefix of ps display.
     */
 
#if defined(PS_USE_SETPROCTITLE) || defined(PS_USE_SETPROCTITLE_FAST)
 
    /*
     * apparently setproctitle() already adds a `progname:' prefix to the ps
     * line
     */
#define PROGRAM_NAME_PREFIX ""
#else
#define PROGRAM_NAME_PREFIX "postgres: "
#endif
 
    if (*cluster_name == '\0')
    {
        snprintf(ps_buffer, ps_buffer_size,
                 PROGRAM_NAME_PREFIX "%s ",
                 fixed_part);
    }
    else
    {
        snprintf(ps_buffer, ps_buffer_size,
                 PROGRAM_NAME_PREFIX "%s: %s ",
                 cluster_name, fixed_part);
    }
 
    ps_buffer_cur_len = ps_buffer_fixed_size = strlen(ps_buffer);
 
    /*
     * On the first run, force the update.
     */
    save_update_process_title = update_process_title;
    update_process_title = true;
    set_ps_display("");
    update_process_title = save_update_process_title;
#endif                          /* not PS_USE_NONE */
}
 
#ifndef PS_USE_NONE
/*
 * update_ps_display_precheck
 *      Helper function to determine if updating the process title is
 *      something that we need to do.
 */
static bool
update_ps_display_precheck(void)
{
    /* update_process_title=off disables updates */
    if (!update_process_title)
        return false;
 
    /* no ps display for stand-alone backend */
    if (!IsUnderPostmaster)
        return false;
 
#ifdef PS_USE_CLOBBER_ARGV
    /* If ps_buffer is a pointer, it might still be null */
    if (!ps_buffer)
        return false;
#endif
 
    return true;
}
#endif                          /* not PS_USE_NONE */
 
/*
 * set_ps_display_suffix
 *      Adjust the process title to append 'suffix' onto the end with a space
 *      between it and the current process title.
 */
void
set_ps_display_suffix(const char *suffix)
{
#ifndef PS_USE_NONE
    size_t      len;
 
    /* first, check if we need to update the process title */
    if (!update_ps_display_precheck())
        return;
 
    /* if there's already a suffix, overwrite it */
    if (ps_buffer_nosuffix_len > 0)
        ps_buffer_cur_len = ps_buffer_nosuffix_len;
    else
        ps_buffer_nosuffix_len = ps_buffer_cur_len;
 
    len = strlen(suffix);
 
    /* check if we have enough space to append the suffix */
    if (ps_buffer_cur_len + len + 1 >= ps_buffer_size)
    {
        /* not enough space.  Check the buffer isn't full already */
        if (ps_buffer_cur_len < ps_buffer_size - 1)
        {
            /* append a space before the suffix */
            ps_buffer[ps_buffer_cur_len++] = ' ';
 
            /* just add what we can and fill the ps_buffer */
            memcpy(ps_buffer + ps_buffer_cur_len, suffix,
                   ps_buffer_size - ps_buffer_cur_len - 1);
            ps_buffer[ps_buffer_size - 1] = '\0';
            ps_buffer_cur_len = ps_buffer_size - 1;
        }
    }
    else
    {
        ps_buffer[ps_buffer_cur_len++] = ' ';
        memcpy(ps_buffer + ps_buffer_cur_len, suffix, len + 1);
        ps_buffer_cur_len = ps_buffer_cur_len + len;
    }
 
    Assert(strlen(ps_buffer) == ps_buffer_cur_len);
 
    /* and set the new title */
    flush_ps_display();
#endif                          /* not PS_USE_NONE */
}
 
/*
 * set_ps_display_remove_suffix
 *      Remove the process display suffix added by set_ps_display_suffix
 */
void
set_ps_display_remove_suffix(void)
{
#ifndef PS_USE_NONE
    /* first, check if we need to update the process title */
    if (!update_ps_display_precheck())
        return;
 
    /* check we added a suffix */
    if (ps_buffer_nosuffix_len == 0)
        return;                 /* no suffix */
 
    /* remove the suffix from ps_buffer */
    ps_buffer[ps_buffer_nosuffix_len] = '\0';
    ps_buffer_cur_len = ps_buffer_nosuffix_len;
    ps_buffer_nosuffix_len = 0;
 
    Assert(ps_buffer_cur_len == strlen(ps_buffer));
 
    /* and set the new title */
    flush_ps_display();
#endif                          /* not PS_USE_NONE */
}
 
/*
 * Call this to update the ps status display to a fixed prefix plus an
 * indication of what you're currently doing passed in the argument.
 *
 * 'len' must be the same as strlen(activity)
 */
void
set_ps_display_with_len(const char *activity, size_t len)
{
    Assert(strlen(activity) == len);
 
#ifndef PS_USE_NONE
    /* first, check if we need to update the process title */
    if (!update_ps_display_precheck())
        return;
 
    /* wipe out any suffix when the title is completely changed */
    ps_buffer_nosuffix_len = 0;
 
    /* Update ps_buffer to contain both fixed part and activity */
    if (ps_buffer_fixed_size + len >= ps_buffer_size)
    {
        /* handle the case where ps_buffer doesn't have enough space */
        memcpy(ps_buffer + ps_buffer_fixed_size, activity,
               ps_buffer_size - ps_buffer_fixed_size - 1);
        ps_buffer[ps_buffer_size - 1] = '\0';
        ps_buffer_cur_len = ps_buffer_size - 1;
    }
    else
    {
        memcpy(ps_buffer + ps_buffer_fixed_size, activity, len + 1);
        ps_buffer_cur_len = ps_buffer_fixed_size + len;
    }
    Assert(strlen(ps_buffer) == ps_buffer_cur_len);
 
    /* Transmit new setting to kernel, if necessary */
    flush_ps_display();
#endif                          /* not PS_USE_NONE */
}
 
#ifndef PS_USE_NONE
static void
flush_ps_display(void)
{
#ifdef PS_USE_SETPROCTITLE
    setproctitle("%s", ps_buffer);
#elif defined(PS_USE_SETPROCTITLE_FAST)
    setproctitle_fast("%s", ps_buffer);
#endif
 
#ifdef PS_USE_CLOBBER_ARGV
    /* pad unused memory; need only clobber remainder of old status string */
    if (last_status_len > ps_buffer_cur_len)
        MemSet(ps_buffer + ps_buffer_cur_len, PS_PADDING,
               last_status_len - ps_buffer_cur_len);
    last_status_len = ps_buffer_cur_len;
#endif                          /* PS_USE_CLOBBER_ARGV */
 
#ifdef PS_USE_WIN32
    {
        /*
         * Win32 does not support showing any changed arguments. To make it at
         * all possible to track which backend is doing what, we create a
         * named object that can be viewed with for example Process Explorer.
         */
        static HANDLE ident_handle = INVALID_HANDLE_VALUE;
        char        name[PS_BUFFER_SIZE + 32];
 
        if (ident_handle != INVALID_HANDLE_VALUE)
            CloseHandle(ident_handle);
 
        sprintf(name, "pgident(%d): %s", MyProcPid, ps_buffer);
 
        ident_handle = CreateEvent(NULL, TRUE, FALSE, name);
    }
#endif                          /* PS_USE_WIN32 */
}
#endif                          /* not PS_USE_NONE */
 
/*
 * Returns what's currently in the ps display, in case someone needs
 * it.  Note that only the activity part is returned.  On some platforms
 * the string will not be null-terminated, so return the effective
 * length into *displen.
 */
const char *
get_ps_display(int *displen)
{
#ifdef PS_USE_CLOBBER_ARGV
    /* If ps_buffer is a pointer, it might still be null */
    if (!ps_buffer)
    {
        *displen = 0;
        return "";
    }
#endif
 
#ifndef PS_USE_NONE
    *displen = (int) (ps_buffer_cur_len - ps_buffer_fixed_size);
 
    return ps_buffer + ps_buffer_fixed_size;
#else
    *displen = 0;
    return "";
#endif
}