src/basic/xattr-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <errno.h>
   4 #include <fcntl.h>
   5 #include <linux/stat.h>
   6 #include <stdint.h>
   7 #include <stdlib.h>
   8 #include <string.h>
   9 #include <sys/time.h>
  10 #include <sys/xattr.h>
  11
  12 #include "alloc-util.h"
  13 #include "fd-util.h"
  14 #include "macro.h"
  15 #include "missing.h"
  16 #include "sparse-endian.h"
  17 #include "stdio-util.h"
  18 #include "string-util.h"
  19 #include "time-util.h"
  20 #include "xattr-util.h"
  21
  22 int getxattr_malloc(const char *path, const char *name, char **value, bool allow_symlink) {
  23         char *v;
  24         size_t l;
  25         ssize_t n;
  26
  27         assert(path);
  28         assert(name);
  29         assert(value);
  30
  31         for (l = 100; ; l = (size_t) n + 1) {
  32                 v = new0(char, l);
  33                 if (!v)
  34                         return -ENOMEM;
  35
  36                 if (allow_symlink)
  37                         n = lgetxattr(path, name, v, l);
  38                 else
  39                         n = getxattr(path, name, v, l);
  40
  41                 if (n >= 0 && (size_t) n < l) {
  42                         *value = v;
  43                         return n;
  44                 }
  45
  46                 free(v);
  47
  48                 if (n < 0 && errno != ERANGE)
  49                         return -errno;
  50
  51                 if (allow_symlink)
  52                         n = lgetxattr(path, name, NULL, 0);
  53                 else
  54                         n = getxattr(path, name, NULL, 0);
  55                 if (n < 0)
  56                         return -errno;
  57         }
  58 }
  59
  60 int fgetxattr_malloc(int fd, const char *name, char **value) {
  61         char *v;
  62         size_t l;
  63         ssize_t n;
  64
  65         assert(fd >= 0);
  66         assert(name);
  67         assert(value);
  68
  69         for (l = 100; ; l = (size_t) n + 1) {
  70                 v = new0(char, l);
  71                 if (!v)
  72                         return -ENOMEM;
  73
  74                 n = fgetxattr(fd, name, v, l);
  75
  76                 if (n >= 0 && (size_t) n < l) {
  77                         *value = v;
  78                         return n;
  79                 }
  80
  81                 free(v);
  82
  83                 if (n < 0 && errno != ERANGE)
  84                         return -errno;
  85
  86                 n = fgetxattr(fd, name, NULL, 0);
  87                 if (n < 0)
  88                         return -errno;
  89         }
  90 }
  91
  92 int fgetxattrat_fake(
  93                 int dirfd,
  94                 const char *filename,
  95                 const char *attribute,
  96                 void *value, size_t size,
  97                 int flags,
  98                 size_t *ret_size) {
  99
 100         char fn[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int) + 1];
 101         _cleanup_close_ int fd = -1;
 102         ssize_t l;
 103
 104         /* The kernel doesn't have a fgetxattrat() command, hence let's emulate one */
 105
 106         if (flags & ~(AT_SYMLINK_NOFOLLOW|AT_EMPTY_PATH))
 107                 return -EINVAL;
 108
 109         if (isempty(filename)) {
 110                 if (!(flags & AT_EMPTY_PATH))
 111                         return -EINVAL;
 112
 113                 xsprintf(fn, "/proc/self/fd/%i", dirfd);
 114         } else {
 115                 fd = openat(dirfd, filename, O_CLOEXEC|O_PATH|(flags & AT_SYMLINK_NOFOLLOW ? O_NOFOLLOW : 0));
 116                 if (fd < 0)
 117                         return -errno;
 118
 119                 xsprintf(fn, "/proc/self/fd/%i", fd);
 120         }
 121
 122         l = getxattr(fn, attribute, value, size);
 123         if (l < 0)
 124                 return -errno;
 125
 126         *ret_size = l;
 127         return 0;
 128 }
 129
 130 static int parse_crtime(le64_t le, usec_t *usec) {
 131         uint64_t u;
 132
 133         assert(usec);
 134
 135         u = le64toh(le);
 136         if (IN_SET(u, 0, (uint64_t) -1))
 137                 return -EIO;
 138
 139         *usec = (usec_t) u;
 140         return 0;
 141 }
 142
 143 int fd_getcrtime_at(int dirfd, const char *name, usec_t *ret, int flags) {
 144         struct_statx sx;
 145         usec_t a, b;
 146         le64_t le;
 147         size_t n;
 148         int r;
 149
 150         assert(ret);
 151
 152         if (flags & ~(AT_EMPTY_PATH|AT_SYMLINK_NOFOLLOW))
 153                 return -EINVAL;
 154
 155         /* So here's the deal: the creation/birth time (crtime/btime) of a file is a relatively newly supported concept
 156          * on Linux (or more strictly speaking: a concept that only recently got supported in the API, it was
 157          * implemented on various file systems on the lower level since a while, but never was accessible). However, we
 158          * needed a concept like that for vaccuuming algorithms and such, hence we emulated it via a user xattr for a
 159          * long time. Starting with Linux 4.11 there's statx() which exposes the timestamp to userspace for the first
 160          * time, where it is available. Thius function will read it, but it tries to keep some compatibility with older
 161          * systems: we try to read both the crtime/btime and the xattr, and then use whatever is older. After all the
 162          * concept is useful for determining how "old" a file really is, and hence using the older of the two makes
 163          * most sense. */
 164
 165         if (statx(dirfd, strempty(name), flags|AT_STATX_DONT_SYNC, STATX_BTIME, &sx) >= 0 &&
 166             (sx.stx_mask & STATX_BTIME) &&
 167             sx.stx_btime.tv_sec != 0)
 168                 a = (usec_t) sx.stx_btime.tv_sec * USEC_PER_SEC +
 169                         (usec_t) sx.stx_btime.tv_nsec / NSEC_PER_USEC;
 170         else
 171                 a = USEC_INFINITY;
 172
 173         r = fgetxattrat_fake(dirfd, name, "user.crtime_usec", &le, sizeof(le), flags, &n);
 174         if (r >= 0) {
 175                 if (n != sizeof(le))
 176                         r = -EIO;
 177                 else
 178                         r = parse_crtime(le, &b);
 179         }
 180         if (r < 0) {
 181                 if (a != USEC_INFINITY) {
 182                         *ret = a;
 183                         return 0;
 184                 }
 185
 186                 return r;
 187         }
 188
 189         if (a != USEC_INFINITY)
 190                 *ret = MIN(a, b);
 191         else
 192                 *ret = b;
 193
 194         return 0;
 195 }
 196
 197 int fd_getcrtime(int fd, usec_t *ret) {
 198         return fd_getcrtime_at(fd, NULL, ret, AT_EMPTY_PATH);
 199 }
 200
 201 int path_getcrtime(const char *p, usec_t *ret) {
 202         return fd_getcrtime_at(AT_FDCWD, p, ret, 0);
 203 }
 204
 205 int fd_setcrtime(int fd, usec_t usec) {
 206         le64_t le;
 207
 208         assert(fd >= 0);
 209
 210         if (IN_SET(usec, 0, USEC_INFINITY))
 211                 usec = now(CLOCK_REALTIME);
 212
 213         le = htole64((uint64_t) usec);
 214         if (fsetxattr(fd, "user.crtime_usec", &le, sizeof(le), 0) < 0)
 215                 return -errno;
 216
 217         return 0;
 218 }