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-rw-r--r--src/basic/xattr-util.c295
1 files changed, 295 insertions, 0 deletions
diff --git a/src/basic/xattr-util.c b/src/basic/xattr-util.c
new file mode 100644
index 0000000..0b661d9
--- /dev/null
+++ b/src/basic/xattr-util.c
@@ -0,0 +1,295 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <sys/time.h>
+#include <sys/xattr.h>
+
+#include "alloc-util.h"
+#include "errno-util.h"
+#include "fd-util.h"
+#include "macro.h"
+#include "missing_syscall.h"
+#include "sparse-endian.h"
+#include "stat-util.h"
+#include "stdio-util.h"
+#include "string-util.h"
+#include "time-util.h"
+#include "xattr-util.h"
+
+int getxattr_at_malloc(
+ int fd,
+ const char *path,
+ const char *name,
+ int flags,
+ char **ret) {
+
+ _cleanup_close_ int opened_fd = -1;
+ unsigned n_attempts = 7;
+ bool by_procfs = false;
+ size_t l = 100;
+
+ assert(fd >= 0 || fd == AT_FDCWD);
+ assert(name);
+ assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0);
+ assert(ret);
+
+ /* So, this is single function that does what getxattr()/lgetxattr()/fgetxattr() does, but in one go,
+ * and with additional bells and whistles. Specifically:
+ *
+ * 1. This works on O_PATH fds (which fgetxattr() does not)
+ * 2. Provides full openat()-style semantics, i.e. by-fd, by-path and combination thereof
+ * 3. As extension to openat()-style semantics implies AT_EMPTY_PATH if path is NULL.
+ * 4. Does a malloc() loop, automatically sizing the allocation
+ * 5. NUL-terminates the returned buffer (for safety)
+ */
+
+ if (!path) /* If path is NULL, imply AT_EMPTY_PATH. – But if it's "", don't — for safety reasons. */
+ flags |= AT_EMPTY_PATH;
+
+ if (isempty(path)) {
+ if (!FLAGS_SET(flags, AT_EMPTY_PATH))
+ return -EINVAL;
+
+ if (fd == AT_FDCWD) /* Both unspecified? Then operate on current working directory */
+ path = ".";
+ else
+ path = NULL;
+
+ } else if (fd != AT_FDCWD) {
+
+ /* If both have been specified, then we go via O_PATH */
+ opened_fd = openat(fd, path, O_PATH|O_CLOEXEC|(FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? 0 : O_NOFOLLOW));
+ if (opened_fd < 0)
+ return -errno;
+
+ fd = opened_fd;
+ path = NULL;
+ by_procfs = true; /* fgetxattr() is not going to work, go via /proc/ link right-away */
+ }
+
+ for (;;) {
+ _cleanup_free_ char *v = NULL;
+ ssize_t n;
+
+ if (n_attempts == 0) /* If someone is racing against us, give up eventually */
+ return -EBUSY;
+ n_attempts--;
+
+ v = new0(char, l+1);
+ if (!v)
+ return -ENOMEM;
+
+ l = MALLOC_ELEMENTSOF(v) - 1;
+
+ if (path)
+ n = FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? getxattr(path, name, v, l) : lgetxattr(path, name, v, l);
+ else
+ n = by_procfs ? getxattr(FORMAT_PROC_FD_PATH(fd), name, v, l) : fgetxattr(fd, name, v, l);
+ if (n < 0) {
+ if (errno == EBADF) {
+ if (by_procfs || path)
+ return -EBADF;
+
+ by_procfs = true; /* Might be an O_PATH fd, try again via /proc/ link */
+ continue;
+ }
+
+ if (errno != ERANGE)
+ return -errno;
+ } else {
+ v[n] = 0; /* NUL terminate */
+ *ret = TAKE_PTR(v);
+ return (int) n;
+ }
+
+ if (path)
+ n = FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? getxattr(path, name, NULL, 0) : lgetxattr(path, name, NULL, 0);
+ else
+ n = by_procfs ? getxattr(FORMAT_PROC_FD_PATH(fd), name, NULL, 0) : fgetxattr(fd, name, NULL, 0);
+ if (n < 0)
+ return -errno;
+ if (n > INT_MAX) /* We couldn't return this as 'int' anymore */
+ return -E2BIG;
+
+ l = (size_t) n;
+ }
+}
+
+static int parse_crtime(le64_t le, usec_t *usec) {
+ uint64_t u;
+
+ assert(usec);
+
+ u = le64toh(le);
+ if (IN_SET(u, 0, UINT64_MAX))
+ return -EIO;
+
+ *usec = (usec_t) u;
+ return 0;
+}
+
+int fd_getcrtime_at(
+ int fd,
+ const char *path,
+ int flags,
+ usec_t *ret) {
+
+ _cleanup_free_ le64_t *le = NULL;
+ STRUCT_STATX_DEFINE(sx);
+ usec_t a, b;
+ int r;
+
+ assert(fd >= 0 || fd == AT_FDCWD);
+ assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0);
+ assert(ret);
+
+ if (!path)
+ flags |= AT_EMPTY_PATH;
+
+ /* So here's the deal: the creation/birth time (crtime/btime) of a file is a relatively newly supported concept
+ * on Linux (or more strictly speaking: a concept that only recently got supported in the API, it was
+ * implemented on various file systems on the lower level since a while, but never was accessible). However, we
+ * needed a concept like that for vaccuuming algorithms and such, hence we emulated it via a user xattr for a
+ * long time. Starting with Linux 4.11 there's statx() which exposes the timestamp to userspace for the first
+ * time, where it is available. Thius function will read it, but it tries to keep some compatibility with older
+ * systems: we try to read both the crtime/btime and the xattr, and then use whatever is older. After all the
+ * concept is useful for determining how "old" a file really is, and hence using the older of the two makes
+ * most sense. */
+
+ if (statx(fd, strempty(path),
+ (flags & ~AT_SYMLINK_FOLLOW)|(FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? 0 : AT_SYMLINK_NOFOLLOW)|AT_STATX_DONT_SYNC,
+ STATX_BTIME,
+ &sx) >= 0 &&
+ (sx.stx_mask & STATX_BTIME) &&
+ sx.stx_btime.tv_sec != 0)
+ a = (usec_t) sx.stx_btime.tv_sec * USEC_PER_SEC +
+ (usec_t) sx.stx_btime.tv_nsec / NSEC_PER_USEC;
+ else
+ a = USEC_INFINITY;
+
+ r = getxattr_at_malloc(fd, path, "user.crtime_usec", flags, (char**) &le);
+ if (r >= 0) {
+ if (r != sizeof(*le))
+ r = -EIO;
+ else
+ r = parse_crtime(*le, &b);
+ }
+ if (r < 0) {
+ if (a != USEC_INFINITY) {
+ *ret = a;
+ return 0;
+ }
+
+ return r;
+ }
+
+ if (a != USEC_INFINITY)
+ *ret = MIN(a, b);
+ else
+ *ret = b;
+
+ return 0;
+}
+
+int fd_setcrtime(int fd, usec_t usec) {
+ le64_t le;
+
+ assert(fd >= 0);
+
+ if (!timestamp_is_set(usec))
+ usec = now(CLOCK_REALTIME);
+
+ le = htole64((uint64_t) usec);
+ return RET_NERRNO(fsetxattr(fd, "user.crtime_usec", &le, sizeof(le), 0));
+}
+
+int listxattr_at_malloc(
+ int fd,
+ const char *path,
+ int flags,
+ char **ret) {
+
+ _cleanup_close_ int opened_fd = -1;
+ bool by_procfs = false;
+ unsigned n_attempts = 7;
+ size_t l = 100;
+
+ assert(fd >= 0 || fd == AT_FDCWD);
+ assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0);
+ assert(ret);
+
+ /* This is to listxattr()/llistattr()/flistattr() what getxattr_at_malloc() is to getxattr()/… */
+
+ if (!path) /* If path is NULL, imply AT_EMPTY_PATH. – But if it's "", don't. */
+ flags |= AT_EMPTY_PATH;
+
+ if (isempty(path)) {
+ if (!FLAGS_SET(flags, AT_EMPTY_PATH))
+ return -EINVAL;
+
+ if (fd == AT_FDCWD) /* Both unspecified? Then operate on current working directory */
+ path = ".";
+ else
+ path = NULL;
+
+ } else if (fd != AT_FDCWD) {
+ /* If both have been specified, then we go via O_PATH */
+ opened_fd = openat(fd, path, O_PATH|O_CLOEXEC|(FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? 0 : O_NOFOLLOW));
+ if (opened_fd < 0)
+ return -errno;
+
+ fd = opened_fd;
+ path = NULL;
+ by_procfs = true;
+ }
+
+ for (;;) {
+ _cleanup_free_ char *v = NULL;
+ ssize_t n;
+
+ if (n_attempts == 0) /* If someone is racing against us, give up eventually */
+ return -EBUSY;
+ n_attempts--;
+
+ v = new(char, l+1);
+ if (!v)
+ return -ENOMEM;
+
+ l = MALLOC_ELEMENTSOF(v) - 1;
+
+ if (path)
+ n = FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? listxattr(path, v, l) : llistxattr(path, v, l);
+ else
+ n = by_procfs ? listxattr(FORMAT_PROC_FD_PATH(fd), v, l) : flistxattr(fd, v, l);
+ if (n < 0) {
+ if (errno == EBADF) {
+ if (by_procfs || path)
+ return -EBADF;
+
+ by_procfs = true; /* Might be an O_PATH fd, try again via /proc/ link */
+ continue;
+ }
+
+ if (errno != ERANGE)
+ return -errno;
+ } else {
+ v[n] = 0; /* NUL terminate */
+ *ret = TAKE_PTR(v);
+ return (int) n;
+ }
+
+ if (path)
+ n = FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? listxattr(path, NULL, 0) : llistxattr(path, NULL, 0);
+ else
+ n = by_procfs ? listxattr(FORMAT_PROC_FD_PATH(fd), NULL, 0) : flistxattr(fd, NULL, 0);
+ if (n < 0)
+ return -errno;
+ if (n > INT_MAX) /* We couldn't return this as 'int' anymore */
+ return -E2BIG;
+
+ l = (size_t) n;
+ }
+}
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