Messages in this thread |  | | | Date | Tue, 3 Mar 2009 22:43:16 -0500 (EST) | | From | Steven Rostedt <> | | Subject | Re: [PATCH 5/5] tracing: add binary buffer files for use with splice |
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On Tue, 3 Mar 2009, Andrew Morton wrote:
> On Tue, 03 Mar 2009 21:49:26 -0500 Steven Rostedt <rostedt@goodmis.org> wrote: > > > +static ssize_t > > +tracing_buffers_read(struct file *filp, char __user *ubuf, > > + size_t count, loff_t *ppos) > > +{ > > + struct ftrace_buffer_info *info = filp->private_data; > > + unsigned int pos; > > + ssize_t ret; > > + size_t size; > > + > > + /* Do we have previous read data to read? */ > > + if (info->read < PAGE_SIZE) > > + goto read; > > + > > + info->read = 0; > > + > > + ret = ring_buffer_read_page(info->tr->buffer, > > + &info->spare, > > + count, > > + info->cpu, 0); > > + if (ret < 0) > > + return 0; > > + > > + pos = ring_buffer_page_len(info->spare); > > + > > + if (pos < PAGE_SIZE) > > + memset(info->spare + pos, 0, PAGE_SIZE - pos); > > + > > +read: > > + size = PAGE_SIZE - info->read; > > + if (size > count) > > + size = count; > > + > > + ret = copy_to_user(ubuf, info->spare + info->read, size); > > + if (ret) > > + return -EFAULT; > > Conventionally a read() system call will return the number of bytes > copied, and will only return -EFOO if the number of bytes copied was > zero. > > Lots of parts of the kernel break this, but it's usually device drivers > and scruffy pseudo files, in which case a partial file read doesn't > make much sense. This doesn't make the broken behaviour right, but at > least we have a bit of a weaselly excuse in that case. >
I just went by the read man page:
EFAULT buf is outside your accessible address space.
-- Steve
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