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 <[email protected]>
---
More context sent earlier this week: https://lore.kernel.org/linux-api/CAGbU3_nVvuzMn2wo4_ZKufWcGfmGsopVujzTWw-Bbeky=xS+GA@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
On Fri, Jul 24, 2020 at 05:40:43PM -0700, Pascal Bouchareine wrote:
> 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
Have you even tried to test it? When will it ever free those things?
On Sat, Jul 25, 2020 at 3:10 PM Al Viro <[email protected]> wrote:
> Have you even tried to test it? When will it ever free those things?
Thanks for pointing that out, I'll try to address that in the thread
I did basic tests against 5.4: set a description, concurrently set it
from multiple child processes, read, demo with ss/netstat.
However I rebased against master and have not tested the build after
rebase, is that broken?
Should I use a different target for tests?
Thanks for your help
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 <[email protected]>
---
Documentation/filesystems/proc.rst | 3 +++
fs/fcntl.c | 19 +++++++++++++++++++
fs/file_table.c | 3 +++
fs/proc/fd.c | 5 +++++
include/linux/fs.h | 3 +++
include/uapi/linux/fcntl.h | 5 +++++
scripts/get_maintainer.pl | 2 ++
7 files changed, 40 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/file_table.c b/fs/file_table.c
index 656647f9575a..f2d9be7b6459 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -272,6 +272,9 @@ static void __fput(struct file *file)
eventpoll_release(file);
locks_remove_file(file);
+ if (file->f_description)
+ 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..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.
diff --git a/scripts/get_maintainer.pl b/scripts/get_maintainer.pl
index 484d2fbf5921..2e7c434b2b2d 100755
--- a/scripts/get_maintainer.pl
+++ b/scripts/get_maintainer.pl
@@ -2309,6 +2309,8 @@ sub vcs_file_blame {
my @commit_signers = ();
my $cmd;
+ print STDERR "checking commit $commit\n";
+
$cmd = $VCS_cmds{"find_commit_signers_cmd"};
$cmd =~ s/(\$\w+)/$1/eeg; #substitute variables in $cmd
--
2.25.1
One intended usage is to allow processes to self-document sockets
for netstat and friends to report
Signed-off-by: Pascal Bouchareine <[email protected]>
---
Documentation/filesystems/proc.rst | 3 +++
fs/fcntl.c | 19 +++++++++++++++++++
fs/file_table.c | 2 ++
fs/proc/fd.c | 5 +++++
include/linux/fs.h | 3 +++
include/uapi/linux/fcntl.h | 5 +++++
6 files changed, 37 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/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..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
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 <[email protected]>
---
Documentation/filesystems/proc.rst | 3 +++
fs/fcntl.c | 19 +++++++++++++++++++
fs/file_table.c | 2 ++
fs/proc/fd.c | 5 +++++
include/linux/fs.h | 3 +++
include/uapi/linux/fcntl.h | 5 +++++
6 files changed, 37 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/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..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
Sorry about all the noise, please disregard this one.
On Sat, Jul 25, 2020 at 7:04 PM Pascal Bouchareine <[email protected]> wrote:
>
> One intended usage is to allow processes to self-document sockets
> for netstat and friends to report
>
> Signed-off-by: Pascal Bouchareine <[email protected]>
> ---
> Documentation/filesystems/proc.rst | 3 +++
> fs/fcntl.c | 19 +++++++++++++++++++
> fs/file_table.c | 2 ++
> fs/proc/fd.c | 5 +++++
> include/linux/fs.h | 3 +++
> include/uapi/linux/fcntl.h | 5 +++++
> 6 files changed, 37 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/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..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
>
On Fri, Jul 24, 2020 at 10:22:36PM -0700, Pascal Bouchareine wrote:
> 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
> +static long fcntl_set_description(struct file *file, char __user *desc)
> +{
> + char *d;
> +
> + d = strndup_user(desc, MAX_FILE_DESC_SIZE);
This should be kmem accounted because allocation is persistent.
To make things more entertaining, strndup_user() doesn't have gfp_t argument.
> + 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);
Generally kfree under spinlock is not good idea.
You can replace the pointer and free without spinlock.
> --- 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;
struct file is nicely aligned to 256 bytes on distro configs.
Will this break everything?
$ cat /sys/kernel/slab/filp/object_size
Thanks for reviewing, I added some questions inline below
On Mon, Jul 27, 2020 at 7:21 AM Alexey Dobriyan <[email protected]> wrote:
> > + d = strndup_user(desc, MAX_FILE_DESC_SIZE);
>
> This should be kmem accounted because allocation is persistent.
> To make things more entertaining, strndup_user() doesn't have gfp_t argument.
I had to look it up so I might be very far from it, but is that
__GFP_ACCOUNT and would it be correct to assume memdup_user() should
use it unconditionally?
Otherwise my simple option would be to implement the logic in the
set_description, but the benefit would be very local.
Please let me know what you think is best, happy to read more doc if
there's a more productive way to address that
>
> > + 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);
>
> Generally kfree under spinlock is not good idea.
> You can replace the pointer and free without spinlock.
Sorry I also need some pointers here - do you suggest I move the kfree
out of the locked section or that there is a safe way other than
spinlock?
> struct file is nicely aligned to 256 bytes on distro configs.
> Will this break everything?
>
> $ cat /sys/kernel/slab/filp/object_size
Indeed on the config I'm using here this jumped to 264 bytes
Would it be better to move this to the inode struct? I don't know the
implications of this - any other option?
Thanks!
On Mon, Jul 27, 2020 at 6:39 PM Pascal Bouchareine <[email protected]> wrote:
> > struct file is nicely aligned to 256 bytes on distro configs.
> > Will this break everything?
> >
> > $ cat /sys/kernel/slab/filp/object_size
>
> Indeed on the config I'm using here this jumped to 264 bytes
>
> Would it be better to move this to the inode struct? I don't know the
> implications of this - any other option?
Well it doesn't actually make much sense to share that at that level
However the above 264 is building from 5.4 without f_sb_err, so I
think master already passed the 256 bytes too ?