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Tue, 31 Mar 2026 10:56:46 -0700 (PDT) Received: from localhost ([2a01:4b00:d036:ae00:5ed5:ec79:be2b:6da8]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-4887e952b0bsm46752035e9.12.2026.03.31.10.56.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2026 10:56:45 -0700 (PDT) From: luca.boccassi@gmail.com To: kexec@lists.infradead.org Cc: linux-mm@kvack.org, graf@amazon.com, rppt@kernel.org, pasha.tatashin@soleen.com, pratyush@kernel.org, Luca Boccassi Subject: [PATCH] liveupdate: add LIVEUPDATE_SESSION_GET_NAME ioctl Date: Tue, 31 Mar 2026 18:55:32 +0100 Message-ID: <20260331175639.4066033-1-luca.boccassi@gmail.com> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: F376E40018 X-Stat-Signature: ot39t8zy74d9h6dcddg4ddxetwin57aj X-HE-Tag: 1774979807-368808 X-HE-Meta: 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 OKtUbJTW 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Luca Boccassi Userspace when requesting a session specifies a name and gets a FD, but then there is no way to go back the other way and get the name given a LUO session FD. This is problematic especially when there is a userspace orchestrator that wants to check what FDs it is handling for clients. Resolving the /proc/self/fd/X is lossy as that has a hard limit of characters, so names might be truncated. Also requiring going through procfs and doing manual string mangling is not a nice pattern. Add a ioctl to simply get the name from an FD. Signed-off-by: Luca Boccassi --- Need this for integration in systemd, so that I can check what FDs I get from clients and what they are, and so that I can know where to hand it back to include/uapi/linux/liveupdate.h | 19 +++++ kernel/liveupdate/luo_session.c | 13 ++++ .../testing/selftests/liveupdate/liveupdate.c | 72 +++++++++++++++++++ 3 files changed, 104 insertions(+) diff --git a/include/uapi/linux/liveupdate.h b/include/uapi/linux/liveupdate.h index 30bc66ee9436a..41dc44d239dde 100644 --- a/include/uapi/linux/liveupdate.h +++ b/include/uapi/linux/liveupdate.h @@ -59,6 +59,7 @@ enum { LIVEUPDATE_CMD_SESSION_PRESERVE_FD = LIVEUPDATE_CMD_SESSION_BASE, LIVEUPDATE_CMD_SESSION_RETRIEVE_FD = 0x41, LIVEUPDATE_CMD_SESSION_FINISH = 0x42, + LIVEUPDATE_CMD_SESSION_GET_NAME = 0x43, }; /** @@ -213,4 +214,22 @@ struct liveupdate_session_finish { #define LIVEUPDATE_SESSION_FINISH \ _IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_FINISH) +/** + * struct liveupdate_session_get_name - ioctl(LIVEUPDATE_SESSION_GET_NAME) + * @size: Input; sizeof(struct liveupdate_session_get_name) + * @name: Output; A null-terminated string with the full session name. + * + * Retrieves the full name of the session associated with this file descriptor. + * This is useful because the kernel may truncate the name shown in /proc. + * + * Return: 0 on success, negative error code on failure. + */ +struct liveupdate_session_get_name { + __u32 size; + __u8 name[LIVEUPDATE_SESSION_NAME_LENGTH]; +}; + +#define LIVEUPDATE_SESSION_GET_NAME \ + _IO(LIVEUPDATE_IOCTL_TYPE, LIVEUPDATE_CMD_SESSION_GET_NAME) + #endif /* _UAPI_LIVEUPDATE_H */ diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c index 4a40c7fdfb44f..819e8864869fd 100644 --- a/kernel/liveupdate/luo_session.c +++ b/kernel/liveupdate/luo_session.c @@ -289,10 +289,21 @@ static int luo_session_finish(struct luo_session *session, return luo_ucmd_respond(ucmd, sizeof(*argp)); } +static int luo_session_get_name(struct luo_session *session, + struct luo_ucmd *ucmd) +{ + struct liveupdate_session_get_name *argp = ucmd->cmd; + + strscpy((char *)argp->name, session->name, sizeof(argp->name)); + + return luo_ucmd_respond(ucmd, sizeof(*argp)); +} + union ucmd_buffer { struct liveupdate_session_finish finish; struct liveupdate_session_preserve_fd preserve; struct liveupdate_session_retrieve_fd retrieve; + struct liveupdate_session_get_name get_name; }; struct luo_ioctl_op { @@ -319,6 +330,8 @@ static const struct luo_ioctl_op luo_session_ioctl_ops[] = { struct liveupdate_session_preserve_fd, token), IOCTL_OP(LIVEUPDATE_SESSION_RETRIEVE_FD, luo_session_retrieve_fd, struct liveupdate_session_retrieve_fd, token), + IOCTL_OP(LIVEUPDATE_SESSION_GET_NAME, luo_session_get_name, + struct liveupdate_session_get_name, name), }; static long luo_session_ioctl(struct file *filep, unsigned int cmd, diff --git a/tools/testing/selftests/liveupdate/liveupdate.c b/tools/testing/selftests/liveupdate/liveupdate.c index c2878e3d5ef90..510a583371fac 100644 --- a/tools/testing/selftests/liveupdate/liveupdate.c +++ b/tools/testing/selftests/liveupdate/liveupdate.c @@ -102,6 +102,22 @@ static int create_session(int lu_fd, const char *name) return args.fd; } +/* Helper function to get a session name via ioctl. */ +static int get_session_name(int session_fd, char *name, size_t name_len) +{ + struct liveupdate_session_get_name args = {}; + + args.size = sizeof(args); + + if (ioctl(session_fd, LIVEUPDATE_SESSION_GET_NAME, &args)) + return -errno; + + strncpy(name, (char *)args.name, name_len - 1); + name[name_len - 1] = '\0'; + + return 0; +} + /* * Test Case: Create Duplicate Session * @@ -345,4 +361,60 @@ TEST_F(liveupdate_device, preserve_unsupported_fd) ASSERT_EQ(close(session_fd), 0); } +/* + * Test Case: Get Session Name + * + * Verifies that the full session name can be retrieved from a session file + * descriptor via ioctl. This is important because /proc may truncate the + * anon_inode name. + */ +TEST_F(liveupdate_device, get_session_name) +{ + char name_buf[LIVEUPDATE_SESSION_NAME_LENGTH] = {}; + const char *session_name = "get-name-test-session"; + int session_fd; + + self->fd1 = open(LIVEUPDATE_DEV, O_RDWR); + if (self->fd1 < 0 && errno == ENOENT) + SKIP(return, "%s does not exist", LIVEUPDATE_DEV); + ASSERT_GE(self->fd1, 0); + + session_fd = create_session(self->fd1, session_name); + ASSERT_GE(session_fd, 0); + + ASSERT_EQ(get_session_name(session_fd, name_buf, sizeof(name_buf)), 0); + ASSERT_STREQ(name_buf, session_name); + + ASSERT_EQ(close(session_fd), 0); +} + +/* + * Test Case: Get Session Name at Maximum Length + * + * Verifies that a session name using the full LIVEUPDATE_SESSION_NAME_LENGTH + * (minus the null terminator) can be correctly retrieved. + */ +TEST_F(liveupdate_device, get_session_name_max_length) +{ + char name_buf[LIVEUPDATE_SESSION_NAME_LENGTH] = {}; + char long_name[LIVEUPDATE_SESSION_NAME_LENGTH]; + int session_fd; + + memset(long_name, 'A', sizeof(long_name) - 1); + long_name[sizeof(long_name) - 1] = '\0'; + + self->fd1 = open(LIVEUPDATE_DEV, O_RDWR); + if (self->fd1 < 0 && errno == ENOENT) + SKIP(return, "%s does not exist", LIVEUPDATE_DEV); + ASSERT_GE(self->fd1, 0); + + session_fd = create_session(self->fd1, long_name); + ASSERT_GE(session_fd, 0); + + ASSERT_EQ(get_session_name(session_fd, name_buf, sizeof(name_buf)), 0); + ASSERT_STREQ(name_buf, long_name); + + ASSERT_EQ(close(session_fd), 0); +} + TEST_HARNESS_MAIN -- 2.47.3