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/* nbdkit
* Copyright Red Hat
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* * Neither the name of Red Hat nor the names of its contributors may be
* used to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
* PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <nbdkit-filter.h>
static const char *ro_file; /* readonly-file, may be NULL */
static int
readonly_config (nbdkit_next_config *next, nbdkit_backend *nxdata,
const char *key, const char *value)
{
if (strcmp (key, "readonly-file") == 0) {
if (ro_file != NULL) {
nbdkit_error ("readonly-file parameter appears multiple times");
return -1;
}
ro_file = value;
return 0;
}
else
return next (nxdata, key, value);
}
#define readonly_config_help \
"readonly-file=FILENAME If FILENAME present, set to readonly"
static void *
readonly_open (nbdkit_next_open *next, nbdkit_context *nxdata,
int readonly, const char *exportname, int is_tls)
{
/* If we're in "permanent readonly mode" then we set the readonly
* flag for the underlying plugin, since that may make it behave
* differently (or more efficiently). We also return false for
* can_write() below. However if we're testing for the file then we
* cannot do that.
*/
if (ro_file == NULL)
readonly = 1;
if (next (nxdata, readonly, exportname) == -1)
return NULL;
return NBDKIT_HANDLE_NOT_NEEDED;
}
static int
readonly_can_write (nbdkit_next *next, void *handle)
{
if (ro_file == NULL)
return 0;
/* We don't have to test if the file is present here, because if we
* did that then the connection would be permanently read-only.
*/
return next->can_write (next);
}
/* This function tests for readonly and injects the error if so.
* Returns true if the operation should be rejected.
*/
static bool
is_readonly_mode (const char *fn, int *err)
{
if (ro_file == NULL || access (ro_file, R_OK) == 0) {
nbdkit_error ("%s operation rejected by readonly filter", fn);
/* This is turned into NBD_EPERM in the server, but keep the more
* descriptive errno in case the NBD protocol expands the range of
* possible errors in future. Also "Read-only file system" is
* printed in the nbdkit log.
*/
*err = EROFS;
return true;
}
return false;
}
static int
readonly_pwrite (nbdkit_next *next,
void *handle,
const void *buf, uint32_t count, uint64_t offset,
uint32_t flags, int *err)
{
if (is_readonly_mode ("pwrite", err)) return -1;
return next->pwrite (next, buf, count, offset, flags, err);
}
static int
readonly_trim (nbdkit_next *next,
void *handle, uint32_t count, uint64_t offset,
uint32_t flags, int *err)
{
if (is_readonly_mode ("trim", err)) return -1;
return next->trim (next, count, offset, flags, err);
}
static int
readonly_zero (nbdkit_next *next,
void *handle, uint32_t count, uint64_t offset,
uint32_t flags, int *err)
{
if (is_readonly_mode ("zero", err)) return -1;
return next->zero (next, count, offset, flags, err);
}
/* Should we catch and deny flush requests? Unclear, but an argument
* can be made that we should not: Even if the disk has just been made
* unwritable, any writes that were issued prior to that should be
* allowed to flush, otherwise you could get inconsistency. Also a
* flush may not actually issue any writes, but it is hard to know
* that from the filter.
*/
static struct nbdkit_filter filter = {
.name = "readonly",
.longname = "nbdkit readonly filter",
.config = readonly_config,
.config_help = readonly_config_help,
.open = readonly_open,
.can_write = readonly_can_write,
.pwrite = readonly_pwrite,
.trim = readonly_trim,
.zero = readonly_zero,
};
NBDKIT_REGISTER_FILTER (filter)
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