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new helper: single_open_size()

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Same as single_open(), but preallocates the buffer of given size.
Doesn't make any sense for sizes up to PAGE_SIZE and doesn't make
sense if output of show() exceeds PAGE_SIZE only rarely - seq_read()
will take care of growing the buffer and redoing show().  If you
_know_ that it will be large, it might make more sense to look into
saner iterator, rather than go with single-shot one.  If that's
impossible, single_open_size() might be for you.

Again, don't use that without a good reason; occasionally that's really
the best way to go, but very often there are better solutions.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2013-03-31 13:43:23 -04:00
parent 70ef457dc9
commit 2043f495c7
2 changed files with 19 additions and 0 deletions
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18
fs/seq_file.c
View File

@ -599,6 +599,24 @@ int single_open(struct file *file, int (*show)(struct seq_file *, void *),
}
EXPORT_SYMBOL(single_open);
int single_open_size(struct file *file, int (*show)(struct seq_file *, void *),
void *data, size_t size)
{
char *buf = kmalloc(size, GFP_KERNEL);
int ret;
if (!buf)
return -ENOMEM;
ret = single_open(file, show, data);
if (ret) {
kfree(buf);
return ret;
}
((struct seq_file *)file->private_data)->buf = buf;
((struct seq_file *)file->private_data)->size = size;
return 0;
}
EXPORT_SYMBOL(single_open_size);
int single_release(struct inode *inode, struct file *file)
{
const struct seq_operations *op = ((struct seq_file *)file->private_data)->op;

1
include/linux/seq_file.h
View File

@ -123,6 +123,7 @@ static inline int seq_nodemask_list(struct seq_file *m, nodemask_t *mask)
}
int single_open(struct file *, int (*)(struct seq_file *, void *), void *);
int single_open_size(struct file *, int (*)(struct seq_file *, void *), void *, size_t);
int single_release(struct inode *, struct file *);
void *__seq_open_private(struct file *, const struct seq_operations *, int);
int seq_open_private(struct file *, const struct seq_operations *, int);