From e5be74c7c23b159aa43c7e6708e46d71a7af677d Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Fri, 19 Feb 2016 16:13:50 +0000 Subject: [PATCH] staging: comedi: COMEDI_BUFINFO: get amount freed, not amount allocated The `COMEDI_BUFINFO` ioctl is used to advance the current position in the buffer by a specified amount (which can be 0) and get the new position. On input, the `bytes_read` member of `struct comedi_bufinfo` specifies the amount to advance the "read" position for an asynchronous command in the "read" direction, and the `bytes_written` member specifies the amount to advance the "write" position for a command in the "write" direction. The handler `do_bufinfo_ioctl()` may limit the specified values according to amount of readable or writable space in the buffer. On output, the `struct comedi_bufinfo` is filled in with the updated position information, along with the adjusted `bytes_read` and `bytes_written` members. Advancing the buffer position occurs in two steps: first, some buffer space is allocated, and second, it is freed, advancing the current "read" or "write" position. Currently, `do_bufinfo_ioctl()` limits `bytes_read` or `bytes_written` to the amount it could allocate in the first step, but that is invisible and irrelevant to the ioctl user. It's mostly irrelevant to the COMEDI internals as well, apart from limiting how much can be freed in the second step. Change it to ignore how much it managed to allocate in the first step and just use the amount that was actually freed in the second step, which is the amount the current buffer position was actually moved by this ioctl call. Signed-off-by: Ian Abbott Signed-off-by: Greg Kroah-Hartman --- drivers/staging/comedi/comedi_fops.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c index d57fadef47fc..2cfb61e0f2b8 100644 --- a/drivers/staging/comedi/comedi_fops.c +++ b/drivers/staging/comedi/comedi_fops.c @@ -1142,8 +1142,8 @@ static int do_bufinfo_ioctl(struct comedi_device *dev, return -EACCES; if (bi.bytes_read && !(async->cmd.flags & CMDF_WRITE)) { - bi.bytes_read = comedi_buf_read_alloc(s, bi.bytes_read); - comedi_buf_read_free(s, bi.bytes_read); + comedi_buf_read_alloc(s, bi.bytes_read); + bi.bytes_read = comedi_buf_read_free(s, bi.bytes_read); if (comedi_is_subdevice_idle(s) && comedi_buf_read_n_available(s) == 0) { @@ -1152,9 +1152,8 @@ static int do_bufinfo_ioctl(struct comedi_device *dev, } if (bi.bytes_written && (async->cmd.flags & CMDF_WRITE)) { - bi.bytes_written = - comedi_buf_write_alloc(s, bi.bytes_written); - comedi_buf_write_free(s, bi.bytes_written); + comedi_buf_write_alloc(s, bi.bytes_written); + bi.bytes_written = comedi_buf_write_free(s, bi.bytes_written); } copyback_position: -- 2.39.5