source: vendor/3.5.4/source3/modules/vfs_syncops.c

/* 
 * ensure meta data operations are performed synchronously
 *
 * Copyright (C) Andrew Tridgell     2007
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *  
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *  
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include "includes.h"

/*

  Some filesystems (even some journaled filesystems) require that a
  fsync() be performed on many meta data operations to ensure that the
  operation is guaranteed to remain in the filesystem after a power
  failure. This is particularly important for some cluster filesystems
  which are participating in a node failover system with clustered
  Samba

  On those filesystems this module provides a way to perform those
  operations safely.  
 */

/*
  most of the performance loss with this module is in fsync on close(). 
  You can disable that with syncops:onclose = no
 */
static bool sync_onclose;

/*
  given a filename, find the parent directory
 */
static char *parent_dir(TALLOC_CTX *mem_ctx, const char *name)
{
        const char *p = strrchr(name, '/');
        if (p == NULL) {
                return talloc_strdup(mem_ctx, ".");
        }
        return talloc_strndup(mem_ctx, name, (p+1) - name);
}

/*
  fsync a directory by name
 */
static void syncops_sync_directory(const char *dname)
{
#ifdef O_DIRECTORY
        int fd = open(dname, O_DIRECTORY|O_RDONLY);
        if (fd != -1) {
                fsync(fd);
                close(fd);
        }
#else
        DIR *d = opendir(dname);
        if (d != NULL) {
                fsync(dirfd(d));
                closedir(d);
        }
#endif
}

/*
  sync two meta data changes for 2 names
 */
static void syncops_two_names(const char *name1, const char *name2)
{
        TALLOC_CTX *tmp_ctx = talloc_new(NULL);
        char *parent1, *parent2;
        parent1 = parent_dir(tmp_ctx, name1);
        parent2 = parent_dir(tmp_ctx, name2);
        if (!parent1 || !parent2) {
                talloc_free(tmp_ctx);
                return;
        }
        syncops_sync_directory(parent1);
        if (strcmp(parent1, parent2) != 0) {
                syncops_sync_directory(parent2);                
        }
        talloc_free(tmp_ctx);
}

/*
  sync two meta data changes for 1 names
 */
static void syncops_name(const char *name)
{
        char *parent;
        parent = parent_dir(NULL, name);
        if (parent) {
                syncops_sync_directory(parent);
                talloc_free(parent);
        }
}

/*
  sync two meta data changes for 1 names
 */
static void syncops_smb_fname(const struct smb_filename *smb_fname)
{
        char *parent;
        parent = parent_dir(NULL, smb_fname->base_name);
        if (parent) {
                syncops_sync_directory(parent);
                talloc_free(parent);
        }
}


/*
  rename needs special handling, as we may need to fsync two directories
 */
static int syncops_rename(vfs_handle_struct *handle,
                          const struct smb_filename *smb_fname_src,
                          const struct smb_filename *smb_fname_dst)
{
        int ret = SMB_VFS_NEXT_RENAME(handle, smb_fname_src, smb_fname_dst);
        if (ret == 0) {
                syncops_two_names(smb_fname_src->base_name,
                                  smb_fname_dst->base_name);
        }
        return ret;
}

/* handle the rest with a macro */
#define SYNCOPS_NEXT(op, fname, args) do {   \
        int ret = SMB_VFS_NEXT_ ## op args; \
        if (ret == 0 && fname) syncops_name(fname); \
        return ret; \
} while (0)

#define SYNCOPS_NEXT_SMB_FNAME(op, fname, args) do {   \
        int ret = SMB_VFS_NEXT_ ## op args; \
        if (ret == 0 && fname) syncops_smb_fname(fname); \
        return ret; \
} while (0)

static int syncops_symlink(vfs_handle_struct *handle,
                           const char *oldname, const char *newname)
{
        SYNCOPS_NEXT(SYMLINK, newname, (handle, oldname, newname));
}

static int syncops_link(vfs_handle_struct *handle,
                         const char *oldname, const char *newname)
{
        SYNCOPS_NEXT(LINK, newname, (handle, oldname, newname));
}

static int syncops_open(vfs_handle_struct *handle,
                        struct smb_filename *smb_fname, files_struct *fsp,
                        int flags, mode_t mode)
{
        SYNCOPS_NEXT_SMB_FNAME(OPEN, (flags&O_CREAT?smb_fname:NULL),
                               (handle, smb_fname, fsp, flags, mode));
}

static int syncops_unlink(vfs_handle_struct *handle,
                          const struct smb_filename *smb_fname)
{
        SYNCOPS_NEXT_SMB_FNAME(UNLINK, smb_fname, (handle, smb_fname));
}

static int syncops_mknod(vfs_handle_struct *handle,
                         const char *fname, mode_t mode, SMB_DEV_T dev)
{
        SYNCOPS_NEXT(MKNOD, fname, (handle, fname, mode, dev));
}

static int syncops_mkdir(vfs_handle_struct *handle,  const char *fname, mode_t mode)
{
        SYNCOPS_NEXT(MKDIR, fname, (handle, fname, mode));
}

static int syncops_rmdir(vfs_handle_struct *handle,  const char *fname)
{
        SYNCOPS_NEXT(RMDIR, fname, (handle, fname));
}

/* close needs to be handled specially */
static int syncops_close(vfs_handle_struct *handle, files_struct *fsp)
{
        if (fsp->can_write && sync_onclose) {
                /* ideally we'd only do this if we have written some
                 data, but there is no flag for that in fsp yet. */
                fsync(fsp->fh->fd);
        }
        return SMB_VFS_NEXT_CLOSE(handle, fsp);
}


static struct vfs_fn_pointers vfs_syncops_fns = {
        .mkdir = syncops_mkdir,
        .rmdir = syncops_rmdir,
        .open = syncops_open,
        .rename = syncops_rename,
        .unlink = syncops_unlink,
        .symlink = syncops_symlink,
        .link = syncops_link,
        .mknod = syncops_mknod,
        .close_fn = syncops_close,
};

NTSTATUS vfs_syncops_init(void)
{
        NTSTATUS ret;

        ret = smb_register_vfs(SMB_VFS_INTERFACE_VERSION, "syncops",
                               &vfs_syncops_fns);

        if (!NT_STATUS_IS_OK(ret))
                return ret;

        sync_onclose = lp_parm_bool(-1, "syncops", "onclose", true);
        
        return ret;
}