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[108.232.117.128]) by smtp.gmail.com with ESMTPSA id k11sm7229460qkk.93.2020.08.13.20.57.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Aug 2020 20:57:17 -0700 (PDT) From: Pascal Bouchareine To: linux-kernel@vger.kernel.org Cc: Pascal Bouchareine , linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, "Andrew Morton" , "Alexey Dobriyan" , "Al Viro" , "Jeff Layton" , "J. Bruce Fields" Subject: [PATCH v4 2/2] fcntl: introduce F_SET_DESCRIPTION Date: Thu, 13 Aug 2020 20:54:53 -0700 Message-Id: <20200814035453.210716-3-kalou@tfz.net> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200814035453.210716-1-kalou@tfz.net> References: <20200814035453.210716-1-kalou@tfz.net> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org This command attaches a description to a file descriptor for troubleshooting purposes. The free string is displayed in the process fdinfo file for that fd /proc/pid/fdinfo/fd. One intended usage is to allow processes to self-document sockets for netstat and friends to report Signed-off-by: Pascal Bouchareine --- fs/fcntl.c | 21 +++++++++++++++++++++ fs/file_table.c | 2 ++ fs/proc/fd.c | 5 +++++ include/linux/fs.h | 3 +++ include/uapi/linux/fcntl.h | 5 +++++ 5 files changed, 36 insertions(+) diff --git a/fs/fcntl.c b/fs/fcntl.c index 2e4c0fa2074b..9fbeaaf02802 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -319,6 +319,24 @@ static long fcntl_rw_hint(struct file *file, unsigned int cmd, } } +static long fcntl_set_description(struct file *file, char __user *desc) +{ + char *d, *old; + + d = strndup_user(desc, MAX_FILE_DESC_SIZE, GFP_KERNEL_ACCOUNT); + if (IS_ERR(d)) + return PTR_ERR(d); + + spin_lock(&file->f_lock); + old = file->f_description; + file->f_description = d; + spin_unlock(&file->f_lock); + + kfree(old); + + return 0; +} + static long do_fcntl(int fd, unsigned int cmd, unsigned long arg, struct file *filp) { @@ -426,6 +444,9 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg, case F_SET_FILE_RW_HINT: err = fcntl_rw_hint(filp, cmd, arg); break; + case F_SET_DESCRIPTION: + err = fcntl_set_description(filp, argp); + break; default: break; } diff --git a/fs/file_table.c b/fs/file_table.c index 656647f9575a..6673a48d2ea1 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -272,6 +272,8 @@ static void __fput(struct file *file) eventpoll_release(file); locks_remove_file(file); + kfree(file->f_description); + ima_file_free(file); if (unlikely(file->f_flags & FASYNC)) { if (file->f_op->fasync) diff --git a/fs/proc/fd.c b/fs/proc/fd.c index 81882a13212d..60b3ff971b2b 100644 --- a/fs/proc/fd.c +++ b/fs/proc/fd.c @@ -57,6 +57,11 @@ static int seq_show(struct seq_file *m, void *v) (long long)file->f_pos, f_flags, real_mount(file->f_path.mnt)->mnt_id); + spin_lock(&file->f_lock); + if (file->f_description) + seq_printf(m, "desc:\t%s\n", file->f_description); + spin_unlock(&file->f_lock); + show_fd_locks(m, file, files); if (seq_has_overflowed(m)) goto out; diff --git a/include/linux/fs.h b/include/linux/fs.h index f5abba86107d..a2a683d603b6 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -980,6 +980,9 @@ struct file { struct address_space *f_mapping; errseq_t f_wb_err; errseq_t f_sb_err; /* for syncfs */ + +#define MAX_FILE_DESC_SIZE 256 + char *f_description; } __randomize_layout __attribute__((aligned(4))); /* lest something weird decides that 2 is OK */ diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h index 2f86b2ad6d7e..465385e52f49 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -55,6 +55,11 @@ #define F_GET_FILE_RW_HINT (F_LINUX_SPECIFIC_BASE + 13) #define F_SET_FILE_RW_HINT (F_LINUX_SPECIFIC_BASE + 14) +/* + * Set file description + */ +#define F_SET_DESCRIPTION (F_LINUX_SPECIFIC_BASE + 15) + /* * Valid hint values for F_{GET,SET}_RW_HINT. 0 is "not set", or can be * used to clear any hints previously set. -- 2.25.1