file_ops.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * file_ops.c
 *    Helper functions for operating on files.
 *
 * Most of the functions in this file are helper functions for writing to
 * the target data directory. The functions check the --dry-run flag, and
 * do nothing if it's enabled. You should avoid accessing the target files
 * directly but if you do, make sure you honor the --dry-run mode!
 *
 * Portions Copyright (c) 2013-2025, PostgreSQL Global Development Group
 *
 *-------------------------------------------------------------------------
 */
#include "postgres_fe.h"
 
#include <sys/stat.h>
#include <dirent.h>
#include <fcntl.h>
#include <unistd.h>
 
#include "common/file_perm.h"
#include "common/file_utils.h"
#include "file_ops.h"
#include "filemap.h"
#include "pg_rewind.h"
 
/*
 * Currently open target file.
 */
static int  dstfd = -1;
static char dstpath[MAXPGPATH] = "";
 
static void create_target_dir(const char *path);
static void remove_target_dir(const char *path);
static void create_target_symlink(const char *path, const char *link);
static void remove_target_symlink(const char *path);
 
static void recurse_dir(const char *datadir, const char *parentpath,
                        process_file_callback_t callback);
 
/*
 * Open a target file for writing. If 'trunc' is true and the file already
 * exists, it will be truncated.
 */
void
open_target_file(const char *path, bool trunc)
{
    int         mode;
 
    if (dry_run)
        return;
 
    if (dstfd != -1 && !trunc &&
        strcmp(path, &dstpath[strlen(datadir_target) + 1]) == 0)
        return;                 /* already open */
 
    close_target_file();
 
    snprintf(dstpath, sizeof(dstpath), "%s/%s", datadir_target, path);
 
    mode = O_WRONLY | O_CREAT | PG_BINARY;
    if (trunc)
        mode |= O_TRUNC;
    dstfd = open(dstpath, mode, pg_file_create_mode);
    if (dstfd < 0)
        pg_fatal("could not open target file \"%s\": %m",
                 dstpath);
}
 
/*
 * Close target file, if it's open.
 */
void
close_target_file(void)
{
    if (dstfd == -1)
        return;
 
    if (close(dstfd) != 0)
        pg_fatal("could not close target file \"%s\": %m",
                 dstpath);
 
    dstfd = -1;
}
 
void
write_target_range(char *buf, off_t begin, size_t size)
{
    size_t      writeleft;
    char       *p;
 
    /* update progress report */
    fetch_done += size;
    progress_report(false);
 
    if (dry_run)
        return;
 
    if (lseek(dstfd, begin, SEEK_SET) == -1)
        pg_fatal("could not seek in target file \"%s\": %m",
                 dstpath);
 
    writeleft = size;
    p = buf;
    while (writeleft > 0)
    {
        ssize_t     writelen;
 
        errno = 0;
        writelen = write(dstfd, p, writeleft);
        if (writelen < 0)
        {
            /* if write didn't set errno, assume problem is no disk space */
            if (errno == 0)
                errno = ENOSPC;
            pg_fatal("could not write file \"%s\": %m",
                     dstpath);
        }
 
        p += writelen;
        writeleft -= writelen;
    }
 
    /* keep the file open, in case we need to copy more blocks in it */
}
 
 
void
remove_target(file_entry_t *entry)
{
    Assert(entry->action == FILE_ACTION_REMOVE);
    Assert(entry->target_exists);
 
    switch (entry->target_type)
    {
        case FILE_TYPE_DIRECTORY:
            remove_target_dir(entry->path);
            break;
 
        case FILE_TYPE_REGULAR:
            remove_target_file(entry->path, false);
            break;
 
        case FILE_TYPE_SYMLINK:
            remove_target_symlink(entry->path);
            break;
 
        case FILE_TYPE_UNDEFINED:
            pg_fatal("undefined file type for \"%s\"", entry->path);
            break;
    }
}
 
void
create_target(file_entry_t *entry)
{
    Assert(entry->action == FILE_ACTION_CREATE);
    Assert(!entry->target_exists);
 
    switch (entry->source_type)
    {
        case FILE_TYPE_DIRECTORY:
            create_target_dir(entry->path);
            break;
 
        case FILE_TYPE_SYMLINK:
            create_target_symlink(entry->path, entry->source_link_target);
            break;
 
        case FILE_TYPE_REGULAR:
            /* can't happen. Regular files are created with open_target_file. */
            pg_fatal("invalid action (CREATE) for regular file");
            break;
 
        case FILE_TYPE_UNDEFINED:
            pg_fatal("undefined file type for \"%s\"", entry->path);
            break;
    }
}
 
/*
 * Remove a file from target data directory.  If missing_ok is true, it
 * is fine for the target file to not exist.
 */
void
remove_target_file(const char *path, bool missing_ok)
{
    char        dstpath[MAXPGPATH];
 
    if (dry_run)
        return;
 
    snprintf(dstpath, sizeof(dstpath), "%s/%s", datadir_target, path);
    if (unlink(dstpath) != 0)
    {
        if (errno == ENOENT && missing_ok)
            return;
 
        pg_fatal("could not remove file \"%s\": %m",
                 dstpath);
    }
}
 
void
truncate_target_file(const char *path, off_t newsize)
{
    char        dstpath[MAXPGPATH];
    int         fd;
 
    if (dry_run)
        return;
 
    snprintf(dstpath, sizeof(dstpath), "%s/%s", datadir_target, path);
 
    fd = open(dstpath, O_WRONLY, pg_file_create_mode);
    if (fd < 0)
        pg_fatal("could not open file \"%s\" for truncation: %m",
                 dstpath);
 
    if (ftruncate(fd, newsize) != 0)
        pg_fatal("could not truncate file \"%s\" to %u: %m",
                 dstpath, (unsigned int) newsize);
 
    close(fd);
}
 
static void
create_target_dir(const char *path)
{
    char        dstpath[MAXPGPATH];
 
    if (dry_run)
        return;
 
    snprintf(dstpath, sizeof(dstpath), "%s/%s", datadir_target, path);
    if (mkdir(dstpath, pg_dir_create_mode) != 0)
        pg_fatal("could not create directory \"%s\": %m",
                 dstpath);
}
 
static void
remove_target_dir(const char *path)
{
    char        dstpath[MAXPGPATH];
 
    if (dry_run)
        return;
 
    snprintf(dstpath, sizeof(dstpath), "%s/%s", datadir_target, path);
    if (rmdir(dstpath) != 0)
        pg_fatal("could not remove directory \"%s\": %m",
                 dstpath);
}
 
static void
create_target_symlink(const char *path, const char *link)
{
    char        dstpath[MAXPGPATH];
 
    if (dry_run)
        return;
 
    snprintf(dstpath, sizeof(dstpath), "%s/%s", datadir_target, path);
    if (symlink(link, dstpath) != 0)
        pg_fatal("could not create symbolic link at \"%s\": %m",
                 dstpath);
}
 
static void
remove_target_symlink(const char *path)
{
    char        dstpath[MAXPGPATH];
 
    if (dry_run)
        return;
 
    snprintf(dstpath, sizeof(dstpath), "%s/%s", datadir_target, path);
    if (unlink(dstpath) != 0)
        pg_fatal("could not remove symbolic link \"%s\": %m",
                 dstpath);
}
 
/*
 * Sync target data directory to ensure that modifications are safely on disk.
 *
 * We do this once, for the whole data directory, for performance reasons.  At
 * the end of pg_rewind's run, the kernel is likely to already have flushed
 * most dirty buffers to disk.  Additionally sync_pgdata uses a two-pass
 * approach when fsync is specified (only initiating writeback in the first
 * pass), which often reduces the overall amount of IO noticeably.
 */
void
sync_target_dir(void)
{
    if (!do_sync || dry_run)
        return;
 
    sync_pgdata(datadir_target, PG_VERSION_NUM, sync_method, true);
}
 
 
/*
 * Read a file into memory. The file to be read is <datadir>/<path>.
 * The file contents are returned in a malloc'd buffer, and *filesize
 * is set to the length of the file.
 *
 * The returned buffer is always zero-terminated; the size of the returned
 * buffer is actually *filesize + 1. That's handy when reading a text file.
 * This function can be used to read binary files as well, you can just
 * ignore the zero-terminator in that case.
 */
char *
slurpFile(const char *datadir, const char *path, size_t *filesize)
{
    int         fd;
    char       *buffer;
    struct stat statbuf;
    char        fullpath[MAXPGPATH];
    int         len;
    int         r;
 
    snprintf(fullpath, sizeof(fullpath), "%s/%s", datadir, path);
 
    if ((fd = open(fullpath, O_RDONLY | PG_BINARY, 0)) == -1)
        pg_fatal("could not open file \"%s\" for reading: %m",
                 fullpath);
 
    if (fstat(fd, &statbuf) < 0)
        pg_fatal("could not open file \"%s\" for reading: %m",
                 fullpath);
 
    len = statbuf.st_size;
 
    buffer = pg_malloc(len + 1);
 
    r = read(fd, buffer, len);
    if (r != len)
    {
        if (r < 0)
            pg_fatal("could not read file \"%s\": %m",
                     fullpath);
        else
            pg_fatal("could not read file \"%s\": read %d of %zu",
                     fullpath, r, (Size) len);
    }
    close(fd);
 
    /* Zero-terminate the buffer. */
    buffer[len] = '\0';
 
    if (filesize)
        *filesize = len;
    return buffer;
}
 
/*
 * Traverse through all files in a data directory, calling 'callback'
 * for each file.
 */
void
traverse_datadir(const char *datadir, process_file_callback_t callback)
{
    recurse_dir(datadir, NULL, callback);
}
 
/*
 * recursive part of traverse_datadir
 *
 * parentpath is the current subdirectory's path relative to datadir,
 * or NULL at the top level.
 */
static void
recurse_dir(const char *datadir, const char *parentpath,
            process_file_callback_t callback)
{
    DIR        *xldir;
    struct dirent *xlde;
    char        fullparentpath[MAXPGPATH];
 
    if (parentpath)
        snprintf(fullparentpath, MAXPGPATH, "%s/%s", datadir, parentpath);
    else
        snprintf(fullparentpath, MAXPGPATH, "%s", datadir);
 
    xldir = opendir(fullparentpath);
    if (xldir == NULL)
        pg_fatal("could not open directory \"%s\": %m",
                 fullparentpath);
 
    while (errno = 0, (xlde = readdir(xldir)) != NULL)
    {
        struct stat fst;
        char        fullpath[MAXPGPATH * 2];
        char        path[MAXPGPATH * 2];
 
        if (strcmp(xlde->d_name, ".") == 0 ||
            strcmp(xlde->d_name, "..") == 0)
            continue;
 
        snprintf(fullpath, sizeof(fullpath), "%s/%s", fullparentpath, xlde->d_name);
 
        if (lstat(fullpath, &fst) < 0)
        {
            if (errno == ENOENT)
            {
                /*
                 * File doesn't exist anymore. This is ok, if the new primary
                 * is running and the file was just removed. If it was a data
                 * file, there should be a WAL record of the removal. If it
                 * was something else, it couldn't have been anyway.
                 *
                 * TODO: But complain if we're processing the target dir!
                 */
            }
            else
                pg_fatal("could not stat file \"%s\": %m",
                         fullpath);
        }
 
        if (parentpath)
            snprintf(path, sizeof(path), "%s/%s", parentpath, xlde->d_name);
        else
            snprintf(path, sizeof(path), "%s", xlde->d_name);
 
        if (S_ISREG(fst.st_mode))
            callback(path, FILE_TYPE_REGULAR, fst.st_size, NULL);
        else if (S_ISDIR(fst.st_mode))
        {
            callback(path, FILE_TYPE_DIRECTORY, 0, NULL);
            /* recurse to handle subdirectories */
            recurse_dir(datadir, path, callback);
        }
        else if (S_ISLNK(fst.st_mode))
        {
            char        link_target[MAXPGPATH];
            int         len;
 
            len = readlink(fullpath, link_target, sizeof(link_target));
            if (len < 0)
                pg_fatal("could not read symbolic link \"%s\": %m",
                         fullpath);
            if (len >= sizeof(link_target))
                pg_fatal("symbolic link \"%s\" target is too long",
                         fullpath);
            link_target[len] = '\0';
 
            callback(path, FILE_TYPE_SYMLINK, 0, link_target);
 
            /*
             * If it's a symlink within pg_tblspc, we need to recurse into it,
             * to process all the tablespaces.  We also follow a symlink if
             * it's for pg_wal.  Symlinks elsewhere are ignored.
             */
            if ((parentpath && strcmp(parentpath, PG_TBLSPC_DIR) == 0) ||
                strcmp(path, "pg_wal") == 0)
                recurse_dir(datadir, path, callback);
        }
    }
 
    if (errno)
        pg_fatal("could not read directory \"%s\": %m",
                 fullparentpath);
 
    if (closedir(xldir))
        pg_fatal("could not close directory \"%s\": %m",
                 fullparentpath);
}