sysfs bin file handling will be merged into the regular file support.
This patch prepares the llseek path.
sysfs currently unconditionally uses seq_lseek() whether the file
supports read or not, which means that sysfs_seq_show() may be used
purely for seeking even if the file doesn't implement read.
sysfs_seq_show() simply doesn't produce any data if sysfs_ops->show()
is not available. This is good enough for write-only files as open()
doesn't allow FMODE_READ if sysfs_ops->show() is not implemented and
seq_lseek() sets f_pos to the requested offset as long as show()
doesn't fail.
However, bin files allow FMODE_READ when ->mmap() is implemented even
if ->read() is not, which means that sysfs_seq_show() would need to
fail if ->read() is not implemented, which is fine for read(2) but
would break lseek(2).
This patch implements sysfs_llseek() which uses seq_lseek() iff read
is implemented. If not, generic_file_llseek() is used instead. This
removes the case where sysfs_seq_show() is used purely for seeking
thus solving the above issue. Plus, it's weird to use seq_seek() when
seq_file isn't being used anyway.
Note that sysfs_llseek() handles both regular and bin files. While
this isn't used yet, it'll allow unifying handling of both types.
Signed-off-by: Tejun Heo <t...@kernel.org>
---
fs/sysfs/file.c | 44 +++++++++++++++++++++++++++++++++++---------
1 file changed, 35 insertions(+), 9 deletions(-)
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 6211dd7..d9109d3 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -54,6 +54,11 @@ struct sysfs_open_file {
struct list_head list;
};
+static bool sysfs_is_bin(struct sysfs_dirent *sd)
+{
+ return sysfs_type(sd) == SYSFS_KOBJ_BIN_ATTR;
+}
+
static struct sysfs_open_file *sysfs_of(struct file *file)
{
return ((struct seq_file *)file->private_data)->private;
@@ -72,6 +77,33 @@ static const struct sysfs_ops *sysfs_file_ops(struct
sysfs_dirent *sd)
}
/*
+ * llseek for sysfs. Use seq_lseek() if read operation is implemented;
+ * otherwise, fall back to generic_file_llseek(). This ensures that
+ * sysfs_seq_show() isn't invoked to seek in a file which doesn't
+ * implemented read.
+ */
+static loff_t sysfs_llseek(struct file *file, loff_t offset, int whence)
+{
+ struct sysfs_open_file *of = sysfs_of(file);
+ bool has_read;
+
+ if (!sysfs_get_active(of->sd))
+ return -ENODEV;
+
+ if (sysfs_is_bin(of->sd))
+ has_read = of->sd->s_bin_attr.bin_attr->read;
+ else
+ has_read = sysfs_file_ops(of->sd)->show;
+
+ sysfs_put_active(of->sd);
+
+ if (has_read)
+ return seq_lseek(file, offset, whence);
+ else
+ return generic_file_llseek(file, offset, whence);
+}
+
+/*
* Reads on sysfs are handled through seq_file, which takes care of hairy
* details like buffering and seeking. The following function pipes
* sysfs_ops->show() result through seq_file.
@@ -104,15 +136,9 @@ static int sysfs_seq_show(struct seq_file *sf, void *v)
of->event = atomic_read(&of->sd->s_attr.open->event);
- /*
- * Lookup @ops and invoke show(). Control may reach here via seq
- * file lseek even if @ops->show() isn't implemented.
- */
+ /* lookup @ops and invoke show() */
ops = sysfs_file_ops(of->sd);
- if (ops->show)
- count = ops->show(kobj, of->sd->s_attr.attr, buf);
- else
- count = 0;
+ count = ops->show(kobj, of->sd->s_attr.attr, buf);
sysfs_put_active(of->sd);
mutex_unlock(&of->mutex);
@@ -465,7 +491,7 @@ EXPORT_SYMBOL_GPL(sysfs_notify);
const struct file_operations sysfs_file_operations = {
.read = seq_read,
.write = sysfs_write_file,
- .llseek = seq_lseek,
+ .llseek = sysfs_llseek,
.open = sysfs_open_file,
.release = sysfs_release,
.poll = sysfs_poll,
--
1.8.3.1
--
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