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Prevent mount tmpfs on existing tmpfs mountpoint

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This commit is contained in:
Troy D. Hanson
2014-06-19 17:18:22 -04:00
parent 3fbb0671dc
commit b9775b0a6e
1 changed files with 61 additions and 27 deletions
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88
utils/ramdisk.c
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@@ -12,14 +12,23 @@
#include <stdlib.h>
#include <unistd.h>
#include "utarray.h"
#include <limits.h>
#define TMPFS_MAGIC 0x01021994
/******************************************************************************
* ramdisk
* ramdisk Troy D. Hanson
*
* a utility with modes to:
* - create a ramdisk,
* - attrition its contents (continually or once)
* - query a ramdisk (see its size and percent full)
* - unmount a ramdisk
*
* The ramdisk used here is the 'tmpfs' filesystem which is not strictly a
* pure RAM device; it can swap under the kernel's discretion. I have also
* noticed that a large ramdisk (say, 6gb on a system with 8gb ram) might
* exhibit 'no space left on device' even when only 50% full. A better
* query mode would show the status (resident, paged, etc) of ramdisk pages.
*****************************************************************************/
/* command line configuration parameters */
@@ -30,23 +39,42 @@ char *ramdisk;
UT_array *dirs;
void usage(char *prog) {
fprintf(stderr, "usage:\n\n");
fprintf(stderr, "Create ramdisk, unless it already exists:\n");
fprintf(stderr, " %%%s -c [-s 10g] [-d dir [-d dir]] /path/to/ramdisk\n", prog);
fprintf(stderr, " size is bytes, or suffixed with k|m|g|%% [def: 50%%]\n");
fprintf(stderr, " [-d dir] are dirs in ramdisk to create (absolute path)\n");
fprintf(stderr, "This utility creates a tmpfs ramdisk on a given mountpount.\n");
fprintf(stderr, "It does nothing if a tmpfs is already mounted on that point.\n");
fprintf(stderr, "\n");
fprintf(stderr, "Query mount point to detect/describe ramdisk\n");
fprintf(stderr, " %%%s -q /path/to/ramdisk\n", prog);
fprintf(stderr, " /proc/mounts lists all the ramdisks (and other disks)\n");
fprintf(stderr,"usage:\n\n");
fprintf(stderr, "-c (create mode):\n");
fprintf(stderr, " %s -c [-s <size>] [-d <dir>] <ramdisk-mount-point>\n", prog);
fprintf(stderr, " -s <size> suffixed with k|m|g|%% [default: 50%%]\n");
fprintf(stderr, " -d <dir> directory to post-create inside ramdisk (repeatable)\n");
fprintf(stderr, "\n");
fprintf(stderr, "Unmount ramdisk\n");
fprintf(stderr, " %%%s -u /path/to/ramdisk\n", prog);
fprintf(stderr, "-q (query mode):\n");
fprintf(stderr, " %s -q <ramdisk-mount-point>\n", prog);
fprintf(stderr, "\n");
fprintf(stderr, "-u (unmount mode):\n");
fprintf(stderr, " %s -u <ramdisk-mount-point>\n", prog);
fprintf(stderr, "\n");
fprintf(stderr, "Examples of creating a ramdisk:\n");
fprintf(stderr, " %s -c -s 1g /mnt/ramdisk\n", prog);
fprintf(stderr, " %s -c -s 1g -d /mnt/ramdisk/in -d /mnt/ramdisk/out /mnt/ramdisk\n", prog);
fprintf(stderr, "\n");
fprintf(stderr, "Note: 'cat /proc/mounts' to see mounted tmpfs ramdisks.\n");
exit(-1);
}
/* Prevent a ramdisk from being mounted at the mount-point of an
* existing ramdisk. This prevents people from accidently stacking tmpfs.
* However it is OK to mount a ramdisk on a subdirectory of another ramdisk. */
int suitable_mountpoint(char *dir, struct stat *sb, struct statfs *sf) {
size_t dlen = strlen(dir);
char pdir[PATH_MAX];
struct stat psb;
if (dlen+4 > PATH_MAX) {
syslog(LOG_ERR, "path too long\n");
return -1;
}
if (stat(ramdisk, sb) == -1) { /* does mount point exist? */
syslog(LOG_ERR, "no mount point %s: %s\n", ramdisk, strerror(errno));
return -1;
@@ -59,6 +87,20 @@ int suitable_mountpoint(char *dir, struct stat *sb, struct statfs *sf) {
syslog(LOG_ERR, "can't statfs %s: %s\n", ramdisk, strerror(errno));
return -1;
}
/* is it already a tmpfs mountpoint? */
memcpy(pdir,dir,dlen+1); strcat(pdir,"/..");
if (stat(pdir, &psb) == -1) {
syslog(LOG_ERR, "can't stat %s: %s\n", pdir, strerror(errno));
return -1;
}
int is_mountpoint = (psb.st_dev == sb->st_dev) ? 0 : 1;
int is_tmpfs = (sf->f_type == TMPFS_MAGIC);
if (is_mountpoint && is_tmpfs) {
//syslog(LOG_INFO, "already a tmpfs mountpoint: %s\n", dir, strerror(errno));
return -2;
}
return 0;
}
@@ -67,8 +109,7 @@ int suitable_mountpoint(char *dir, struct stat *sb, struct statfs *sf) {
#define GB (1024*1024*1024L)
int query_ramdisk(void) {
struct stat sb; struct statfs sf;
if (suitable_mountpoint(ramdisk, &sb, &sf) == -1) return -1;
if (sf.f_type != TMPFS_MAGIC) {
if (suitable_mountpoint(ramdisk, &sb, &sf) != -2) {
printf("%s: not a ramdisk\n", ramdisk);
return -1;
}
@@ -84,8 +125,7 @@ int query_ramdisk(void) {
int unmount_ramdisk(void) {
struct stat sb; struct statfs sf;
if (suitable_mountpoint(ramdisk, &sb, &sf) == -1) return -1;
if (sf.f_type != TMPFS_MAGIC) {
if (suitable_mountpoint(ramdisk, &sb, &sf) != -2) {
syslog(LOG_ERR,"%s: not a ramdisk\n", ramdisk);
return -1;
}
@@ -97,23 +137,17 @@ int unmount_ramdisk(void) {
}
int create_ramdisk(void) {
int rc=-1;
int rc;
char opts[100];
struct stat sb; struct statfs sf;
if (suitable_mountpoint(ramdisk, &sb, &sf) == -1) goto done;
if (sf.f_type == TMPFS_MAGIC) { rc=1; goto done; } /* already a ramdisk? */
rc = suitable_mountpoint(ramdisk, &sb, &sf);
if (rc) return rc;
/* ok, mount a ramdisk on this point */
snprintf(opts,sizeof(opts),"size=%s",sz);
if ( (rc=mount("unused", ramdisk, "tmpfs", MS_NOATIME|MS_NODEV, opts))==-1) {
syslog(LOG_ERR, "can't make ramdisk %s: %s\n", ramdisk, strerror(errno));
}
done:
if (rc == 0) syslog(LOG_INFO,"mounted ramdisk %s (size %s)\n", ramdisk, sz);
else if (rc == 1) syslog(LOG_INFO,"ramdisk %s exists\n", ramdisk);
else if (rc == -1) syslog(LOG_ERR,"failed to make ramdisk %s\n", ramdisk);
rc=mount("none", ramdisk, "tmpfs", MS_NOATIME|MS_NODEV, opts);
if (rc) syslog(LOG_ERR, "can't make ramdisk %s: %s\n", ramdisk, strerror(errno));
return rc;
}