diff options
Diffstat (limited to 'src/shared/path-util.c')
| -rw-r--r-- | src/shared/path-util.c | 274 |
1 files changed, 216 insertions, 58 deletions
diff --git a/src/shared/path-util.c b/src/shared/path-util.c index b9db7f1047..be50a1865d 100644 --- a/src/shared/path-util.c +++ b/src/shared/path-util.c @@ -19,15 +19,12 @@ along with systemd; If not, see <http://www.gnu.org/licenses/>. ***/ -#include <assert.h> #include <string.h> #include <unistd.h> #include <errno.h> #include <stdlib.h> -#include <signal.h> #include <stdio.h> #include <fcntl.h> -#include <dirent.h> #include <sys/statvfs.h> #include "macro.h" @@ -36,6 +33,7 @@ #include "strv.h" #include "path-util.h" #include "missing.h" +#include "fileio.h" bool path_is_absolute(const char *p) { return p[0] == '/'; @@ -403,12 +401,18 @@ char* path_startswith(const char *path, const char *prefix) { } } -bool path_equal(const char *a, const char *b) { +int path_compare(const char *a, const char *b) { + int d; + assert(a); assert(b); - if ((a[0] == '/') != (b[0] == '/')) - return false; + /* A relative path and an abolute path must not compare as equal. + * Which one is sorted before the other does not really matter. + * Here a relative path is ordered before an absolute path. */ + d = (a[0] == '/') - (b[0] == '/'); + if (d) + return d; for (;;) { size_t j, k; @@ -417,25 +421,40 @@ bool path_equal(const char *a, const char *b) { b += strspn(b, "/"); if (*a == 0 && *b == 0) - return true; + return 0; - if (*a == 0 || *b == 0) - return false; + /* Order prefixes first: "/foo" before "/foo/bar" */ + if (*a == 0) + return -1; + if (*b == 0) + return 1; j = strcspn(a, "/"); k = strcspn(b, "/"); - if (j != k) - return false; + /* Alphabetical sort: "/foo/aaa" before "/foo/b" */ + d = memcmp(a, b, MIN(j, k)); + if (d) + return (d > 0) - (d < 0); /* sign of d */ - if (memcmp(a, b, j) != 0) - return false; + /* Sort "/foo/a" before "/foo/aaa" */ + d = (j > k) - (j < k); /* sign of (j - k) */ + if (d) + return d; a += j; b += k; } } +bool path_equal(const char *a, const char *b) { + return path_compare(a, b) == 0; +} + +bool path_equal_or_files_same(const char *a, const char *b) { + return path_equal(a, b) || files_same(a, b) > 0; +} + char* path_join(const char *root, const char *path, const char *rest) { assert(path); @@ -452,87 +471,192 @@ char* path_join(const char *root, const char *path, const char *rest) { NULL); } -int path_is_mount_point(const char *t, bool allow_symlink) { +static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *mnt_id) { + char path[strlen("/proc/self/fdinfo/") + DECIMAL_STR_MAX(int)]; + _cleanup_free_ char *fdinfo = NULL; + _cleanup_close_ int subfd = -1; + char *p; + int r; + + if ((flags & AT_EMPTY_PATH) && isempty(filename)) + xsprintf(path, "/proc/self/fdinfo/%i", fd); + else { + subfd = openat(fd, filename, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_PATH); + if (subfd < 0) + return -errno; + + xsprintf(path, "/proc/self/fdinfo/%i", subfd); + } + + r = read_full_file(path, &fdinfo, NULL); + if (r == -ENOENT) /* The fdinfo directory is a relatively new addition */ + return -EOPNOTSUPP; + if (r < 0) + return -errno; + + p = startswith(fdinfo, "mnt_id:"); + if (!p) { + p = strstr(fdinfo, "\nmnt_id:"); + if (!p) /* The mnt_id field is a relatively new addition */ + return -EOPNOTSUPP; + + p += 8; + } - union file_handle_union h = FILE_HANDLE_INIT; + p += strspn(p, WHITESPACE); + p[strcspn(p, WHITESPACE)] = 0; + + return safe_atoi(p, mnt_id); +} + +int fd_is_mount_point(int fd, const char *filename, int flags) { + union file_handle_union h = FILE_HANDLE_INIT, h_parent = FILE_HANDLE_INIT; int mount_id = -1, mount_id_parent = -1; - _cleanup_free_ char *parent = NULL; + bool nosupp = false, check_st_dev = true; struct stat a, b; int r; - bool nosupp = false; - /* We are not actually interested in the file handles, but - * name_to_handle_at() also passes us the mount ID, hence use - * it but throw the handle away */ + assert(fd >= 0); + assert(filename); - if (path_equal(t, "/")) - return 1; - - r = name_to_handle_at(AT_FDCWD, t, &h.handle, &mount_id, allow_symlink ? AT_SYMLINK_FOLLOW : 0); + /* First we will try the name_to_handle_at() syscall, which + * tells us the mount id and an opaque file "handle". It is + * not supported everywhere though (kernel compile-time + * option, not all file systems are hooked up). If it works + * the mount id is usually good enough to tell us whether + * something is a mount point. + * + * If that didn't work we will try to read the mount id from + * /proc/self/fdinfo/<fd>. This is almost as good as + * name_to_handle_at(), however, does not return the the + * opaque file handle. The opaque file handle is pretty useful + * to detect the root directory, which we should always + * consider a mount point. Hence we use this only as + * fallback. Exporting the mnt_id in fdinfo is a pretty recent + * kernel addition. + * + * As last fallback we do traditional fstat() based st_dev + * comparisons. This is how things were traditionally done, + * but unionfs breaks breaks this since it exposes file + * systems with a variety of st_dev reported. Also, btrfs + * subvolumes have different st_dev, even though they aren't + * real mounts of their own. */ + + r = name_to_handle_at(fd, filename, &h.handle, &mount_id, flags); if (r < 0) { if (errno == ENOSYS) /* This kernel does not support name_to_handle_at() - * fall back to the traditional stat() logic. */ - goto fallback; + * fall back to simpler logic. */ + goto fallback_fdinfo; else if (errno == EOPNOTSUPP) /* This kernel or file system does not support - * name_to_handle_at(), hence fallback to the + * name_to_handle_at(), hence let's see if the + * upper fs supports it (in which case it is a + * mount point), otherwise fallback to the * traditional stat() logic */ nosupp = true; - else if (errno == ENOENT) - return 0; else return -errno; } - r = path_get_parent(t, &parent); - if (r < 0) - return r; - - h.handle.handle_bytes = MAX_HANDLE_SZ; - r = name_to_handle_at(AT_FDCWD, parent, &h.handle, &mount_id_parent, AT_SYMLINK_FOLLOW); - if (r < 0) - if (errno == EOPNOTSUPP) + r = name_to_handle_at(fd, "", &h_parent.handle, &mount_id_parent, AT_EMPTY_PATH); + if (r < 0) { + if (errno == EOPNOTSUPP) { if (nosupp) /* Neither parent nor child do name_to_handle_at()? We have no choice but to fall back. */ - goto fallback; + goto fallback_fdinfo; else - /* The parent can't do name_to_handle_at() but - * the directory we are interested in can? - * Or the other way around? + /* The parent can't do name_to_handle_at() but the + * directory we are interested in can? * If so, it must be a mount point. */ return 1; - else + } else return -errno; - else - return mount_id != mount_id_parent; + } -fallback: - if (allow_symlink) - r = stat(t, &a); - else - r = lstat(t, &a); + /* The parent can do name_to_handle_at() but the + * directory we are interested in can't? If so, it + * must be a mount point. */ + if (nosupp) + return 1; - if (r < 0) { - if (errno == ENOENT) - return 0; + /* If the file handle for the directory we are + * interested in and its parent are identical, we + * assume this is the root directory, which is a mount + * point. */ + + if (h.handle.handle_bytes == h_parent.handle.handle_bytes && + h.handle.handle_type == h_parent.handle.handle_type && + memcmp(h.handle.f_handle, h_parent.handle.f_handle, h.handle.handle_bytes) == 0) + return 1; + + return mount_id != mount_id_parent; + +fallback_fdinfo: + r = fd_fdinfo_mnt_id(fd, filename, flags, &mount_id); + if (r == -EOPNOTSUPP) + goto fallback_fstat; + if (r < 0) + return r; + + r = fd_fdinfo_mnt_id(fd, "", AT_EMPTY_PATH, &mount_id_parent); + if (r < 0) + return r; + + if (mount_id != mount_id_parent) + return 1; + /* Hmm, so, the mount ids are the same. This leaves one + * special case though for the root file system. For that, + * let's see if the parent directory has the same inode as we + * are interested in. Hence, let's also do fstat() checks now, + * too, but avoid the st_dev comparisons, since they aren't + * that useful on unionfs mounts. */ + check_st_dev = false; + +fallback_fstat: + /* yay for fstatat() taking a different set of flags than the other + * _at() above */ + if (flags & AT_SYMLINK_FOLLOW) + flags &= ~AT_SYMLINK_FOLLOW; + else + flags |= AT_SYMLINK_NOFOLLOW; + if (fstatat(fd, filename, &a, flags) < 0) return -errno; - } - free(parent); - parent = NULL; + if (fstatat(fd, "", &b, AT_EMPTY_PATH) < 0) + return -errno; + + /* A directory with same device and inode as its parent? Must + * be the root directory */ + if (a.st_dev == b.st_dev && + a.st_ino == b.st_ino) + return 1; + + return check_st_dev && (a.st_dev != b.st_dev); +} + +/* flags can be AT_SYMLINK_FOLLOW or 0 */ +int path_is_mount_point(const char *t, int flags) { + _cleanup_close_ int fd = -1; + _cleanup_free_ char *parent = NULL; + int r; + + assert(t); + + if (path_equal(t, "/")) + return 1; r = path_get_parent(t, &parent); if (r < 0) return r; - r = stat(parent, &b); - if (r < 0) + fd = openat(AT_FDCWD, parent, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_PATH); + if (fd < 0) return -errno; - return a.st_dev != b.st_dev; + return fd_is_mount_point(fd, basename(t), flags); } int path_is_read_only_fs(const char *path) { @@ -683,3 +807,37 @@ int fsck_exists(const char *fstype) { return 0; } + +char *prefix_root(const char *root, const char *path) { + char *n, *p; + size_t l; + + /* If root is passed, prefixes path with it. Otherwise returns + * it as is. */ + + assert(path); + + /* First, drop duplicate prefixing slashes from the path */ + while (path[0] == '/' && path[1] == '/') + path++; + + if (isempty(root) || path_equal(root, "/")) + return strdup(path); + + l = strlen(root) + 1 + strlen(path) + 1; + + n = new(char, l); + if (!n) + return NULL; + + p = stpcpy(n, root); + + while (p > n && p[-1] == '/') + p--; + + if (path[0] != '/') + *(p++) = '/'; + + strcpy(p, path); + return n; +} |