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Date: Sun, 14 Feb 2016 09:19:43 +0100
From: Nicolai Stange <nicstange@...il.com>
To: Julia Lawall <julia.lawall@...6.fr>
Cc: Nicolai Stange <nicstange@...il.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
Jonathan Corbet <corbet@....net>, Jan Kara <jack@...e.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Gilles Muller <Gilles.Muller@...6.fr>,
Nicolas Palix <nicolas.palix@...g.fr>,
Michal Marek <mmarek@...e.com>, linux-kernel@...r.kernel.org,
cocci@...teme.lip6.fr
Subject: Re: [PATCH v3 3/7] debugfs: add support for self-protecting attribute file fops
Julia Lawall <julia.lawall@...6.fr> writes:
> On Sun, 14 Feb 2016, Nicolai Stange wrote:
>
>> In order to protect them against file removal issues, debugfs_create_file()
>> creates a lifetime managing proxy around each struct file_operations
>> handed in.
>>
>> In cases where this struct file_operations is able to manage file lifetime
>> by itself already, the proxy created by debugfs is a waste of resources.
>>
>> The most common class of struct file_operations given to debugfs are those
>> defined by means of the DEFINE_SIMPLE_ATTRIBUTE() macro.
>>
>> Introduce a DEFINE_DEBUGFS_ATTRIBUTE() macro to allow any
>> struct file_operations of this class to be easily made file lifetime aware
>> and thus, to be operated unproxied.
>>
>> Specifically, introduce debugfs_attr_read() and debugfs_attr_write()
>> which wrap simple_attr_read() and simple_attr_write() under the protection
>> of a debugfs_use_file_start()/debugfs_use_file_finish() pair.
>>
>> Make DEFINE_DEBUGFS_ATTRIBUTE() set the defined struct file_operations'
>> ->read() and ->write() members to these wrappers.
>>
>> Export debugfs_create_file_unsafe() in order to allow debugfs users to
>> create their files in non-proxying operation mode.
>>
>> Finally, add a Coccinelle script chasing down possible candidates
>> for a DEFINE_SIMPLE_ATTRIBUTE()/debugfs_create_file() to
>> DEFINE_DEBUGFS_ATTRIBUTE()/debugfs_create_file_unsafe() migration.
>>
>> Signed-off-by: Nicolai Stange <nicstange@...il.com>
>> ---
>> fs/debugfs/file.c | 28 +++++++++
>> fs/debugfs/inode.c | 28 +++++++++
>> include/linux/debugfs.h | 26 +++++++++
>> .../api/debugfs/debugfs_simple_attr.cocci | 68 ++++++++++++++++++++++
>
> Shouldn't the .cocci file be in a different patch, since it has a
> different maintainer?
Certainly. I'll split this off in v4. Before resending I'll wait for
other reviews though.
Is the .cocci file itself Ok in that it matches the expected
style/conventions?
Thank you,
Nicolai
>> 4 files changed, 150 insertions(+)
>> create mode 100644 scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
>>
>> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
>> index f638dbc..2da5fb0 100644
>> --- a/fs/debugfs/file.c
>> +++ b/fs/debugfs/file.c
>> @@ -285,6 +285,34 @@ const struct file_operations debugfs_full_proxy_file_operations = {
>> .open = full_proxy_open,
>> };
>>
>> +ssize_t debugfs_attr_read(struct file *file, char __user *buf,
>> + size_t len, loff_t *ppos)
>> +{
>> + ssize_t ret;
>> + int srcu_idx;
>> +
>> + ret = debugfs_use_file_start(F_DENTRY(file), &srcu_idx);
>> + if (likely(!ret))
>> + ret = simple_attr_read(file, buf, len, ppos);
>> + debugfs_use_file_finish(srcu_idx);
>> + return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(debugfs_attr_read);
>> +
>> +ssize_t debugfs_attr_write(struct file *file, const char __user *buf,
>> + size_t len, loff_t *ppos)
>> +{
>> + ssize_t ret;
>> + int srcu_idx;
>> +
>> + ret = debugfs_use_file_start(F_DENTRY(file), &srcu_idx);
>> + if (likely(!ret))
>> + ret = simple_attr_write(file, buf, len, ppos);
>> + debugfs_use_file_finish(srcu_idx);
>> + return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(debugfs_attr_write);
>> +
>> static struct dentry *debugfs_create_mode(const char *name, umode_t mode,
>> struct dentry *parent, void *value,
>> const struct file_operations *fops,
>> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
>> index 42a9b34..f95e355 100644
>> --- a/fs/debugfs/inode.c
>> +++ b/fs/debugfs/inode.c
>> @@ -368,6 +368,33 @@ struct dentry *debugfs_create_file(const char *name, umode_t mode,
>> }
>> EXPORT_SYMBOL_GPL(debugfs_create_file);
>>
>> +/**
>> + * debugfs_create_file_unsafe - create a file in the debugfs filesystem
>> + * @name: a pointer to a string containing the name of the file to create.
>> + * @mode: the permission that the file should have.
>> + * @parent: a pointer to the parent dentry for this file. This should be a
>> + * directory dentry if set. If this parameter is NULL, then the
>> + * file will be created in the root of the debugfs filesystem.
>> + * @data: a pointer to something that the caller will want to get to later
>> + * on. The inode.i_private pointer will point to this value on
>> + * the open() call.
>> + * @fops: a pointer to a struct file_operations that should be used for
>> + * this file.
>> + *
>> + * debugfs_create_file_unsafe() is completely analogous to
>> + * debugfs_create_file(), the only difference being that the fops
>> + * handed it will not get protected against file removals by the
>> + * debugfs core.
>> + *
>> + * It is your responsibility to protect your struct file_operation
>> + * methods against file removals by means of debugfs_use_file_start()
>> + * and debugfs_use_file_finish(). ->open() is still protected by
>> + * debugfs though.
>> + *
>> + * Any struct file_operations defined by means of
>> + * DEFINE_DEBUGFS_ATTRIBUTE() is protected against file removals and
>> + * thus, may be used here.
>> + */
>> struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,
>> struct dentry *parent, void *data,
>> const struct file_operations *fops)
>> @@ -378,6 +405,7 @@ struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,
>> &debugfs_noop_file_operations,
>> fops);
>> }
>> +EXPORT_SYMBOL_GPL(debugfs_create_file_unsafe);
>>
>> /**
>> * debugfs_create_file_size - create a file in the debugfs filesystem
>> diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
>> index 6d45ae6..c880fe9 100644
>> --- a/include/linux/debugfs.h
>> +++ b/include/linux/debugfs.h
>> @@ -50,6 +50,9 @@ extern struct srcu_struct debugfs_srcu;
>> struct dentry *debugfs_create_file(const char *name, umode_t mode,
>> struct dentry *parent, void *data,
>> const struct file_operations *fops);
>> +struct dentry *debugfs_create_file_unsafe(const char *name, umode_t mode,
>> + struct dentry *parent, void *data,
>> + const struct file_operations *fops);
>>
>> struct dentry *debugfs_create_file_size(const char *name, umode_t mode,
>> struct dentry *parent, void *data,
>> @@ -74,6 +77,26 @@ int debugfs_use_file_start(const struct dentry *dentry, int *srcu_idx)
>>
>> void debugfs_use_file_finish(int srcu_idx) __releases(&debugfs_srcu);
>>
>> +ssize_t debugfs_attr_read(struct file *file, char __user *buf,
>> + size_t len, loff_t *ppos);
>> +ssize_t debugfs_attr_write(struct file *file, const char __user *buf,
>> + size_t len, loff_t *ppos);
>> +
>> +#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt) \
>> +static int __fops ## _open(struct inode *inode, struct file *file) \
>> +{ \
>> + __simple_attr_check_format(__fmt, 0ull); \
>> + return simple_attr_open(inode, file, __get, __set, __fmt); \
>> +} \
>> +static const struct file_operations __fops = { \
>> + .owner = THIS_MODULE, \
>> + .open = __fops ## _open, \
>> + .release = simple_attr_release, \
>> + .read = debugfs_attr_read, \
>> + .write = debugfs_attr_write, \
>> + .llseek = generic_file_llseek, \
>> +}
>> +
>> struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
>> struct dentry *new_dir, const char *new_name);
>>
>> @@ -183,6 +206,9 @@ static int debugfs_use_file_start(const struct dentry *dentry, int *srcu_idx)
>> static void debugfs_use_file_finish(int srcu_idx) __releases(&debugfs_srcu)
>> { }
>>
>> +#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt) \
>> + static const struct file_operations __fops = { 0 }
>> +
>> static inline struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
>> struct dentry *new_dir, char *new_name)
>> {
>> diff --git a/scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci b/scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
>> new file mode 100644
>> index 0000000..bdc418d
>> --- /dev/null
>> +++ b/scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
>> @@ -0,0 +1,68 @@
>> +///
>> +/// Use DEFINE_DEBUGFS_ATTRIBUTE rather than DEFINE_SIMPLE_ATTRIBUTE
>> +/// for debugfs files.
>> +///
>> +/// Rationale: DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file()
>> +/// imposes some significant overhead as compared to
>> +/// DEFINE_DEBUGFS_ATTRIBUTE + debugfs_create_file_unsafe().
>> +///
>> +// Copyright (C): 2016 Nicolai Stange
>> +// Options: --no-includes
>> +//
>> +
>> +virtual context
>> +virtual patch
>> +virtual org
>> +virtual report
>> +
>> +@dsa@
>> +declarer name DEFINE_SIMPLE_ATTRIBUTE;
>> +identifier dsa_fops;
>> +expression dsa_get, dsa_set, dsa_fmt;
>> +position p;
>> +@@
>> +DEFINE_SIMPLE_ATTRIBUTE@p(dsa_fops, dsa_get, dsa_set, dsa_fmt);
>> +
>> +@dcf@
>> +expression name, mode, parent, data;
>> +identifier dsa.dsa_fops;
>> +@@
>> +debugfs_create_file(name, mode, parent, data, &dsa_fops)
>> +
>> +
>> +@...text_dsa depends on context && dcf@
>> +declarer name DEFINE_DEBUGFS_ATTRIBUTE;
>> +identifier dsa.dsa_fops;
>> +expression dsa.dsa_get, dsa.dsa_set, dsa.dsa_fmt;
>> +@@
>> +* DEFINE_SIMPLE_ATTRIBUTE(dsa_fops, dsa_get, dsa_set, dsa_fmt);
>> +
>> +
>> +@...ch_dcf depends on patch expression@
>> +expression name, mode, parent, data;
>> +identifier dsa.dsa_fops;
>> +@@
>> +- debugfs_create_file(name, mode, parent, data, &dsa_fops)
>> ++ debugfs_create_file_unsafe(name, mode, parent, data, &dsa_fops)
>> +
>> +@...ch_dsa depends on patch_dcf && patch@
>> +identifier dsa.dsa_fops;
>> +expression dsa.dsa_get, dsa.dsa_set, dsa.dsa_fmt;
>> +@@
>> +- DEFINE_SIMPLE_ATTRIBUTE(dsa_fops, dsa_get, dsa_set, dsa_fmt);
>> ++ DEFINE_DEBUGFS_ATTRIBUTE(dsa_fops, dsa_get, dsa_set, dsa_fmt);
>> +
>> +
>> +@...ipt:python depends on org && dcf@
>> +fops << dsa.dsa_fops;
>> +p << dsa.p;
>> +@@
>> +msg="%s should be defined with DEFINE_DEBUGFS_ATTRIBUTE" % (fops)
>> +coccilib.org.print_todo(p[0], msg)
>> +
>> +@...ipt:python depends on report && dcf@
>> +fops << dsa.dsa_fops;
>> +p << dsa.p;
>> +@@
>> +msg="WARNING: %s should be defined with DEFINE_DEBUGFS_ATTRIBUTE" % (fops)
>> +coccilib.report.print_report(p[0], msg)
>> --
>> 2.7.1
>>
>>
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