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 <ka...@tfz.net> --- More context sent earlier this week: https://lore.kernel.org/linux-api/CAGbU3_nVvuzMn2wo4_ZKufWcGfmGsopVujzTWw-Bbeky=xs...@mail.gmail.com/T/#u Documentation/filesystems/proc.rst | 3 +++ fs/fcntl.c | 19 +++++++++++++++++++ fs/proc/fd.c | 5 +++++ include/linux/fs.h | 3 +++ include/uapi/linux/fcntl.h | 5 +++++ 5 files changed, 35 insertions(+) diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 996f3cfe7030..ae8045650836 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -1918,6 +1918,9 @@ A typical output is:: flags: 0100002 mnt_id: 19 +An optional 'desc' is set if the process documented its usage of +the file via the fcntl command F_SET_DESCRIPTION. + All locks associated with a file descriptor are shown in its fdinfo too:: lock: 1: FLOCK ADVISORY WRITE 359 00:13:11691 0 EOF diff --git a/fs/fcntl.c b/fs/fcntl.c index 2e4c0fa2074b..c1ef724a906e 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -319,6 +319,22 @@ static long fcntl_rw_hint(struct file *file, unsigned int cmd, } } +static long fcntl_set_description(struct file *file, char __user *desc) +{ + char *d; + + d = strndup_user(desc, MAX_FILE_DESC_SIZE); + if (IS_ERR(d)) + return PTR_ERR(d); + + spin_lock(&file->f_lock); + kfree(file->f_description); + file->f_description = d; + spin_unlock(&file->f_lock); + + return 0; +} + static long do_fcntl(int fd, unsigned int cmd, unsigned long arg, struct file *filp) { @@ -426,6 +442,9 @@ 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/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..09717bfa4e3b 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..f86ff6dc45c7 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
