Merge pull request #31713 from YHNdnzj/pidref-equal

pidref: use fd_inode_same to compare pidfds

src/basic/pidref.c

@@ -8,6 +8,33 @@
 #include "pidref.h"
 #include "process-util.h"
 #include "signal-util.h"
+#include "stat-util.h"
+
+bool pidref_equal(const PidRef *a, const PidRef *b) {
+        int r;
+
+        if (pidref_is_set(a)) {
+                if (!pidref_is_set(b))
+                        return false;
+
+                if (a->pid != b->pid)
+                        return false;
+
+                if (a->fd < 0 || b->fd < 0)
+                        return true;
+
+                /* pidfds live in their own pidfs and each process comes with a unique inode number since
+                 * kernel 6.8. We can safely do this on older kernels too though, as previously anonymous
+                 * inode was used and inode number was the same for all pidfds. */
+                r = fd_inode_same(a->fd, b->fd);
+                if (r < 0)
+                        log_debug_errno(r, "Failed to check whether pidfds for pid " PID_FMT " are equal, assuming yes: %m",
+                                        a->pid);
+                return r != 0;
+        }
+
+        return !pidref_is_set(b);
+}
 
 int pidref_set_pid(PidRef *pidref, pid_t pid) {
         int fd;

src/basic/pidref.h

@@ -19,17 +19,7 @@ static inline bool pidref_is_set(const PidRef *pidref) {
         return pidref && pidref->pid > 0;
 }
 
-static inline bool pidref_equal(const PidRef *a, const PidRef *b) {
-
-        if (pidref_is_set(a)) {
-                if (!pidref_is_set(b))
-                        return false;
-
-                return a->pid == b->pid;
-        }
-
-        return !pidref_is_set(b);
-}
+bool pidref_equal(const PidRef *a, const PidRef *b);
 
 /* This turns a pid_t into a PidRef structure, and acquires a pidfd for it, if possible. (As opposed to
  * PIDREF_MAKE_FROM_PID() above, which does not acquire a pidfd.) */

src/basic/stat-util.c

@@ -365,7 +365,7 @@ bool stat_inode_same(const struct stat *a, const struct stat *b) {
          * a thorough check, comparing inode nr, backing device and if the inode is still of the same type. */
 
         return a && b &&
-                (a->st_mode & S_IFMT) != 0 && /* We use the check for .st_mode if the structure was ever initialized */
+                a->st_dev != 0 && /* is the structure ever initialized? */
                 ((a->st_mode ^ b->st_mode) & S_IFMT) == 0 &&  /* same inode type */
                 a->st_dev == b->st_dev &&
                 a->st_ino == b->st_ino;
@@ -395,7 +395,6 @@ bool statx_inode_same(const struct statx *a, const struct statx *b) {
 
         return a && b &&
                 FLAGS_SET(a->stx_mask, STATX_TYPE|STATX_INO) && FLAGS_SET(b->stx_mask, STATX_TYPE|STATX_INO) &&
-                (a->stx_mode & S_IFMT) != 0 &&
                 ((a->stx_mode ^ b->stx_mode) & S_IFMT) == 0 &&
                 a->stx_dev_major == b->stx_dev_major &&
                 a->stx_dev_minor == b->stx_dev_minor &&

src/basic/stat-util.h

@@ -47,10 +47,12 @@ static inline int null_or_empty_path(const char *fn) {
 int path_is_read_only_fs(const char *path);
 
 int inode_same_at(int fda, const char *filea, int fdb, const char *fileb, int flags);
-
 static inline int inode_same(const char *filea, const char *fileb, int flags) {
         return inode_same_at(AT_FDCWD, filea, AT_FDCWD, fileb, flags);
 }
+static inline int fd_inode_same(int fda, int fdb) {
+        return inode_same_at(fda, NULL, fdb, NULL, AT_EMPTY_PATH);
+}
 
 /* The .f_type field of struct statfs is really weird defined on
  * different archs. Let's give its type a name. */

src/shared/ptyfwd.c

@@ -884,7 +884,7 @@ int pty_forward_new(
 
                 assert(f->input_fd >= 0);
 
-                same = inode_same_at(f->input_fd, NULL, f->output_fd, NULL, AT_EMPTY_PATH);
+                same = fd_inode_same(f->input_fd, f->output_fd);
                 if (same < 0)
                         return same;