Messages in this thread | | | Date | Wed, 06 Aug 2014 16:56:55 +0100 | From | Rob Jones <> | Subject | Re: [PATCH] seq_file: Allow private data to be supplied on seq_open |
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Does anyone have any feedback on this?
I would have thought it was quite uncontroversial.
On 29/07/14 18:39, Rob Jones wrote: > Create a function seq_open_priv() that is identical to seq_open() except > that it accepts a void * parameter that it stores in the private field > of the struct seq_file. > > Document seq_open_priv(). > > Some consumers of the seq_file interface need to pass data to their > iterators that is best obtained at the time the seq_file is opened. > > At the moment these consumers have to obtain the struct seq_file pointer > (stored by seq_open() in file->private_data) and then store a pointer to > their own data in the private field of the struct seq_file so that it > can be accessed by the iterator functions. > > Although this is not a long piece of code it is unneccessary boilerplate. > > seq_open() remains in place and its behaviour remains unchanged so no > existing code should be broken by this patch. > > Signed-off-by: Ian Molton <ian.molton@codethink.co.uk> > Signed-off-by: Rob Jones <rob.jones@codethink.co.uk> > --- > Documentation/filesystems/seq_file.txt | 9 +++++++++ > fs/seq_file.c | 30 ++++++++++++++++++++++++++++-- > include/linux/seq_file.h | 1 + > 3 files changed, 38 insertions(+), 2 deletions(-) > > diff --git a/Documentation/filesystems/seq_file.txt b/Documentation/filesystems/seq_file.txt > index a1e2e0d..128ffee 100644 > --- a/Documentation/filesystems/seq_file.txt > +++ b/Documentation/filesystems/seq_file.txt > @@ -226,6 +226,15 @@ be used for more than one file, you can store an arbitrary pointer in the > private field of the seq_file structure; that value can then be retrieved > by the iterator functions. > > +There is also a function seq_open_priv() which behaves identically to > +seq_open() except that it takes an additional void * parameter that it > +stores in the private field of the seq_file structure, thereby making it > +available to the start function and thus all subsequent iterator functions > +Note that a corresponding wrapper function for seq_release() may need to > +be created to free any resources allocated by an open function that uses > +this capability (although, for simple cases, seq_release_private() may > +suffice). > + > The other operations of interest - read(), llseek(), and release() - are > all implemented by the seq_file code itself. So a virtual file's > file_operations structure will look like: > diff --git a/fs/seq_file.c b/fs/seq_file.c > index 1d641bb..9a0db94 100644 > --- a/fs/seq_file.c > +++ b/fs/seq_file.c > @@ -31,9 +31,10 @@ static void seq_set_overflow(struct seq_file *m) > } > > /** > - * seq_open - initialize sequential file > + * seq_open_priv - initialize sequential file with private data > * @file: file we initialize > * @op: method table describing the sequence > + * @d: private data to be made available to the iterator functions > * > * seq_open() sets @file, associating it with a sequence described > * by @op. @op->start() sets the iterator up and returns the first > @@ -43,8 +44,12 @@ static void seq_set_overflow(struct seq_file *m) > * ERR_PTR(error). In the end of sequence they return %NULL. ->show() > * returns 0 in case of success and negative number in case of error. > * Returning SEQ_SKIP means "discard this element and move on". > + * > + * Supplying @d allows data that is only available at the time the file > + * is opened to be supplied to @op->start() (and thereby to @op->next() > + * as well). > */ > -int seq_open(struct file *file, const struct seq_operations *op) > +int seq_open_priv(struct file *file, const struct seq_operations *op, void *d) > { > struct seq_file *p = file->private_data; > > @@ -57,6 +62,7 @@ int seq_open(struct file *file, const struct seq_operations *op) > memset(p, 0, sizeof(*p)); > mutex_init(&p->lock); > p->op = op; > + p->private = d; > #ifdef CONFIG_USER_NS > p->user_ns = file->f_cred->user_ns; > #endif > @@ -80,6 +86,26 @@ int seq_open(struct file *file, const struct seq_operations *op) > file->f_mode &= ~FMODE_PWRITE; > return 0; > } > +EXPORT_SYMBOL(seq_open_priv); > + > +/** > + * seq_open - initialize sequential file > + * @file: file we initialize > + * @op: method table describing the sequence > + * > + * seq_open() sets @file, associating it with a sequence described > + * by @op. @op->start() sets the iterator up and returns the first > + * element of sequence. @op->stop() shuts it down. @op->next() > + * returns the next element of sequence. @op->show() prints element > + * into the buffer. In case of error ->start() and ->next() return > + * ERR_PTR(error). In the end of sequence they return %NULL. ->show() > + * returns 0 in case of success and negative number in case of error. > + * Returning SEQ_SKIP means "discard this element and move on". > + */ > +int seq_open(struct file *file, const struct seq_operations *op) > +{ > + return seq_open_priv(file, op, NULL); > +} > EXPORT_SYMBOL(seq_open); > > static int traverse(struct seq_file *m, loff_t offset) > diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h > index 52e0097..fce87af 100644 > --- a/include/linux/seq_file.h > +++ b/include/linux/seq_file.h > @@ -95,6 +95,7 @@ static inline void seq_setwidth(struct seq_file *m, size_t size) > void seq_pad(struct seq_file *m, char c); > > char *mangle_path(char *s, const char *p, const char *esc); > +int seq_open_priv(struct file *, const struct seq_operations *, void *); > int seq_open(struct file *, const struct seq_operations *); > ssize_t seq_read(struct file *, char __user *, size_t, loff_t *); > loff_t seq_lseek(struct file *, loff_t, int); >
-- Rob Jones Codethink Ltd mailto:rob.jones@codethink.co.uk tel:+44 161 236 5575
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