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Add support for btrfs subvolumes for user homes

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new switch added to useradd command, --btrfs-subvolume-home. When
specified *and* the filesystem is detected as btrfs, it will create a
subvolume for user's home instead of a plain directory. This is done via
`btrfs subvolume` command.  Specifying the new switch while trying to
create home on non-btrfs will result in an error.

userdel -r will handle and remove this subvolume transparently via
`btrfs subvolume` command. Previosuly this failed as you can't rmdir a
subvolume.

usermod, when moving user's home across devices, will detect if the home
is a subvolume and issue an error messages instead of copying it. Moving
user's home (as subvolume) on same btrfs works transparently.
This commit is contained in:
Adam Majer 2019-01-21 09:32:36 +01:00 committed by Serge Hallyn
parent caefe9e8de
commit c1d36a8acb
6 changed files with 158 additions and 2 deletions
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6
lib/prototypes.h
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@ -72,6 +72,12 @@ extern int expire (const struct passwd *, /*@null@*/const struct spwd *);
/* isexpired.c */
extern int isexpired (const struct passwd *, /*@null@*/const struct spwd *);
/* btrfs.c */
extern int btrfs_create_subvolume(const char *path);
extern int btrfs_remove_subvolume(const char *path);
extern int btrfs_is_subvolume(const char *path);
extern int is_btrfs(const char *path);
/* basename() renamed to Basename() to avoid libc name space confusion */
/* basename.c */
extern /*@observer@*/const char *Basename (const char *str);

1
libmisc/Makefile.am
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@ -10,6 +10,7 @@ libmisc_a_SOURCES = \
age.c \
audit_help.c \
basename.c \
btrfs.c \
chkname.c \
chkname.h \
chowndir.c \

94
libmisc/btrfs.c Normal file
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@ -0,0 +1,94 @@
#include <linux/btrfs_tree.h>
#include <linux/magic.h>
#include <sys/statfs.h>
#include "prototypes.h"
static int run_btrfs_subvolume_cmd(const char *subcmd, const char *arg1, const char *arg2)
{
int status = 0;
const char *cmd = "/sbin/btrfs";
const char *argv[] = {
strrchr(cmd, '/'),
"subvolume",
subcmd,
arg1,
arg2,
NULL
};
if (argv[0] == NULL)
argv[0] = cmd;
else
argv[0] = argv[0] + 1;
if (access(cmd, X_OK)) {
return 1;
}
if (run_command(cmd, argv, NULL, &status))
return -1;
return status;
}
int btrfs_create_subvolume(const char *path)
{
return run_btrfs_subvolume_cmd("create", path, NULL);
}
int btrfs_remove_subvolume(const char *path)
{
return run_btrfs_subvolume_cmd("delete", "-C", path);
}
/* Adapted from btrfsprogs */
/*
* This intentionally duplicates btrfs_util_is_subvolume_fd() instead of opening
* a file descriptor and calling it, because fstat() and fstatfs() don't accept
* file descriptors opened with O_PATH on old kernels (before v3.6 and before
* v3.12, respectively), but stat() and statfs() can be called on a path that
* the user doesn't have read or write permissions to.
*
* returns:
* 1 - btrfs subvolume
* 0 - not btrfs subvolume
* -1 - error
*/
int btrfs_is_subvolume(const char *path)
{
struct stat st;
int ret;
ret = is_btrfs(path);
if (ret <= 0)
return ret;
ret = stat(path, &st);
if (ret == -1)
return -1;
if (st.st_ino != BTRFS_FIRST_FREE_OBJECTID || !S_ISDIR(st.st_mode)) {
return 0;
}
return 1;
}
/* Adapted from btrfsprogs */
int is_btrfs(const char *path)
{
struct statfs sfs;
int ret;
ret = statfs(path, &sfs);
if (ret == -1)
return -1;
return sfs.f_type == BTRFS_SUPER_MAGIC;
}

36
src/useradd.c
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@ -165,6 +165,7 @@ static bool
oflg = false, /* permit non-unique user ID to be specified with -u */
rflg = false, /* create a system account */
sflg = false, /* shell program for new account */
subvolflg = false, /* create subvolume home on BTRFS */
uflg = false, /* specify user ID for new account */
Uflg = false; /* create a group having the same name as the user */
@ -822,6 +823,7 @@ static void usage (int status)
Prog, Prog, Prog);
(void) fputs (_(" -b, --base-dir BASE_DIR base directory for the home directory of the\n"
" new account\n"), usageout);
(void) fputs (_(" --btrfs-subvolume-home use BTRFS subvolume for home directory\n"), usageout);
(void) fputs (_(" -c, --comment COMMENT GECOS field of the new account\n"), usageout);
(void) fputs (_(" -d, --home-dir HOME_DIR home directory of the new account\n"), usageout);
(void) fputs (_(" -D, --defaults print or change default useradd configuration\n"), usageout);
@ -1102,6 +1104,7 @@ static void process_flags (int argc, char **argv)
int c;
static struct option long_options[] = {
{"base-dir", required_argument, NULL, 'b'},
{"btrfs-subvolume-home", no_argument, NULL, 200},
{"comment", required_argument, NULL, 'c'},
{"home-dir", required_argument, NULL, 'd'},
{"defaults", no_argument, NULL, 'D'},
@ -1148,6 +1151,9 @@ static void process_flags (int argc, char **argv)
def_home = optarg;
bflg = true;
break;
case 200:
subvolflg = true;
break;
case 'c':
if (!VALID (optarg)) {
fprintf (stderr,
@ -2073,7 +2079,35 @@ static void create_home (void)
strcat (path, "/");
strcat (path, cp);
if (access (path, F_OK) != 0) {
if (mkdir (path, 0) != 0) {
/* Check if parent directory is BTRFS, fail if requesting
subvolume but no BTRFS. The paths cound be different by the
trailing slash
*/
if (subvolflg && (strlen(prefix_user_home) - (int)strlen(path)) <= 1) {
char *btrfs_check = strdup(path);
if (!btrfs_check) {
fprintf (stderr,
_("%s: error while duplicating string in BTRFS check %s\n"),
Prog, path);
fail_exit (E_HOMEDIR);
}
btrfs_check[strlen(path) - strlen(cp) - 1] = '\0';
if (is_btrfs(btrfs_check) <= 0) {
fprintf (stderr,
_("%s: home directory \"%s\" must be mounted on BTRFS\n"),
Prog, path);
fail_exit (E_HOMEDIR);
}
// make subvolume to mount for user instead of directory
if (btrfs_create_subvolume(path)) {
fprintf (stderr,
_("%s: failed to create BTRFS subvolume: %s\n"),
Prog, path);
fail_exit (E_HOMEDIR);
}
}
else if (mkdir (path, 0) != 0) {
fprintf (stderr,
_("%s: cannot create directory %s\n"),
Prog, path);

16
src/userdel.c
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@ -1272,7 +1272,21 @@ int main (int argc, char **argv)
#endif /* EXTRA_CHECK_HOME_DIR */
if (rflg) {
if (remove_tree (user_home, true) != 0) {
int is_subvolume = btrfs_is_subvolume (user_home);
if (is_subvolume < 0) {
errors++;
/* continue */
}
else if (is_subvolume > 0) {
if (btrfs_remove_subvolume (user_home)) {
fprintf (stderr,
_("%s: error removing subvolume %s\n"),
Prog, user_home);
errors++;
/* continue */
}
}
else if (remove_tree (user_home, true) != 0) {
fprintf (stderr,
_("%s: error removing directory %s\n"),
Prog, user_home);

7
src/usermod.c
View File

@ -1819,6 +1819,13 @@ static void move_home (void)
return;
} else {
if (EXDEV == errno) {
if (btrfs_is_subvolume (prefix_user_home) > 0) {
fprintf (stderr,
_("%s: error: cannot move subvolume from %s to %s - different device\n"),
Prog, prefix_user_home, prefix_user_newhome);
fail_exit (E_HOMEDIR);
}
if (copy_tree (prefix_user_home, prefix_user_newhome, true,
true,
user_id,