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Sun, 12 Oct 2025 04:27:27 -0700 (PDT) From: Askar Safin To: luca.boccassi@gmail.com Cc: alx@kernel.org, brauner@kernel.org, cyphar@cyphar.com, linux-fsdevel@vger.kernel.org, linux-man@vger.kernel.org, safinaskar@gmail.com Subject: Re: [PATCH] man/man2/move_mount.2: document EINVAL on multiple instances Date: Sun, 12 Oct 2025 14:27:21 +0300 Message-ID: <20251012112721.44974-1-safinaskar@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Luca Boccassi : > IIRC Christian said this was working as intended? Just fsmount() to > create a detached mount, and then try to apply it multiple times with > multiple move_mount(), and the second and subsequent ones will fail > with EINVAL I just tested current mainline kernel (67029a49db6c). And move_mount doesn't return EINVAL in this case (move_mount succeds). This means that either EINVAL is not intended, either current mainline kernel is buggy. I tested this in Qemu in very minimal environment (rdinit=/bin/busybox sh). See C source below. -- Askar Safin #include #include #include #include #include #include #define ASSERT(cond) if (!(cond)) { \ fprintf (stderr, "%s: assertion failed\n", #cond); \ exit (1); \ } #define ASSERT_ERRNO(cond) if (!(cond)) { \ fprintf (stderr, "%d: ", __LINE__); \ perror (#cond); \ exit (1); \ } int main (void) { ASSERT_ERRNO (mkdir ("/a", 0777) == 0); ASSERT_ERRNO (mkdir ("/b", 0777) == 0); ASSERT_ERRNO (mkdir ("/c", 0777) == 0); { { int fsfd = fsopen ("tmpfs", 0); ASSERT_ERRNO (fsfd != -1); ASSERT_ERRNO (fsconfig (fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0) == 0); { int mntfd = fsmount (fsfd, 0, 0); ASSERT_ERRNO (mntfd != -1); ASSERT_ERRNO (move_mount (mntfd, "", AT_FDCWD, "/a", MOVE_MOUNT_F_EMPTY_PATH) == 0); ASSERT_ERRNO (move_mount (mntfd, "", AT_FDCWD, "/b", MOVE_MOUNT_F_EMPTY_PATH) == 0); ASSERT_ERRNO (move_mount (mntfd, "", AT_FDCWD, "/c", MOVE_MOUNT_F_EMPTY_PATH) == 0); ASSERT_ERRNO (close (mntfd) == 0); } ASSERT_ERRNO (close (fsfd) == 0); } ASSERT_ERRNO (umount ("/c") == 0); } }