diff options
| -rw-r--r-- | Documentation/filesystems/sysfs.txt | 9 | ||||
| -rw-r--r-- | fs/sysfs/file.c | 5 |
2 files changed, 9 insertions, 5 deletions
diff --git a/Documentation/filesystems/sysfs.txt b/Documentation/filesystems/sysfs.txt index 4598ef7b622b..7f27b8f840d0 100644 --- a/Documentation/filesystems/sysfs.txt +++ b/Documentation/filesystems/sysfs.txt @@ -176,8 +176,10 @@ implementations: Recall that an attribute should only be exporting one value, or an array of similar values, so this shouldn't be that expensive. - This allows userspace to do partial reads and seeks arbitrarily over - the entire file at will. + This allows userspace to do partial reads and forward seeks + arbitrarily over the entire file at will. If userspace seeks back to + zero or does a pread(2) with an offset of '0' the show() method will + be called again, rearmed, to fill the buffer. - On write(2), sysfs expects the entire buffer to be passed during the first write. Sysfs then passes the entire buffer to the store() @@ -192,6 +194,9 @@ implementations: Other notes: +- Writing causes the show() method to be rearmed regardless of current + file position. + - The buffer will always be PAGE_SIZE bytes in length. On i386, this is 4096. diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c index a859c32ff93a..ade9a7e6a757 100644 --- a/fs/sysfs/file.c +++ b/fs/sysfs/file.c @@ -129,7 +129,7 @@ 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) { + if (buffer->needs_read_fill || *ppos == 0) { retval = fill_read_buffer(file->f_path.dentry,buffer); if (retval) goto out; @@ -410,8 +410,7 @@ static int sysfs_release(struct inode *inode, struct file *filp) * return POLLERR|POLLPRI, and select will return the fd whether * it is waiting for read, write, or exceptions. * Once poll/select indicates that the value has changed, you - * need to close and re-open the file, as simply seeking and reading - * again will not get new data, or reset the state of 'poll'. + * need to close and re-open the file, or seek to 0 and read again. * Reminder: this only works for attributes which actively support * it, and it is not possible to test an attribute from userspace * to see if it supports poll (Neither 'poll' nor 'select' return |