From aea585ef8fa6516395022e9d2fed6ec5014128bc Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 1 Oct 2013 17:41:56 -0400 Subject: [PATCH] sysfs: remove sysfs_buffer->needs_read_fill ->needs_read_fill is used to implement the following behaviors. 1. Ensure buffer filling on the first read. 2. Force buffer filling after a write. 3. Force buffer filling after a successful poll. However, #2 and #3 don't really work as sysfs doesn't reset file position. While the read buffer would be refilled, the next read would continue from the position after the last read or write, requiring an explicit seek to the start for it to be useful, which makes ->needs_read_fill superflous as read buffer is always refilled if f_pos == 0. Update sysfs_read_file() to test buffer->page for #1 instead and remove ->needs_read_fill. While this changes behavior in extreme corner cases - e.g. re-reading a sysfs file after seeking to non-zero position after a write or poll, it's highly unlikely to lead to actual breakage. This change is to prepare for using seq_file in the read path. While at it, reformat a comment in fill_write_buffer(). Signed-off-by: Tejun Heo Cc: Kay Sievers Signed-off-by: Greg Kroah-Hartman --- fs/sysfs/file.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c index 81e3f727833f..e2fafc0a9b36 100644 --- a/fs/sysfs/file.c +++ b/fs/sysfs/file.c @@ -47,7 +47,6 @@ struct sysfs_buffer { char *page; const struct sysfs_ops *ops; struct mutex mutex; - int needs_read_fill; int event; struct list_head list; }; @@ -95,12 +94,10 @@ static int fill_read_buffer(struct dentry *dentry, struct sysfs_buffer *buffer) /* Try to struggle along */ count = PAGE_SIZE - 1; } - if (count >= 0) { - buffer->needs_read_fill = 0; + if (count >= 0) buffer->count = count; - } else { + else ret = count; - } return ret; } @@ -130,7 +127,11 @@ sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos) ssize_t retval = 0; mutex_lock(&buffer->mutex); - if (buffer->needs_read_fill || *ppos == 0) { + /* + * Fill on zero offset and the first read so that silly things like + * "dd bs=1 skip=N" can work on sysfs files. + */ + if (*ppos == 0 || !buffer->page) { retval = fill_read_buffer(file->f_path.dentry, buffer); if (retval) goto out; @@ -166,14 +167,15 @@ static int fill_write_buffer(struct sysfs_buffer *buffer, if (count >= PAGE_SIZE) count = PAGE_SIZE - 1; error = copy_from_user(buffer->page, buf, count); - buffer->needs_read_fill = 1; - /* if buf is assumed to contain a string, terminate it by \0, - so e.g. sscanf() can scan the string easily */ + + /* + * If buf is assumed to contain a string, terminate it by \0, so + * e.g. sscanf() can scan the string easily. + */ buffer->page[count] = 0; return error ? -EFAULT : count; } - /** * flush_write_buffer - push buffer to kobject. * @dentry: dentry to the attribute @@ -368,7 +370,6 @@ static int sysfs_open_file(struct inode *inode, struct file *file) goto err_out; mutex_init(&buffer->mutex); - buffer->needs_read_fill = 1; buffer->ops = ops; file->private_data = buffer; @@ -435,7 +436,6 @@ static unsigned int sysfs_poll(struct file *filp, poll_table *wait) return DEFAULT_POLLMASK; trigger: - buffer->needs_read_fill = 1; return DEFAULT_POLLMASK|POLLERR|POLLPRI; }