Re: [RFC][PATCH 1/3] trace_seq: Move the trace_seq code to lib/

Steven Rostedt
2014-06-20T20:51:49Z

On Fri, 20 Jun 2014 16:28:45 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 20 Jun 2014 10:12:44 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
>
>
> > > > > +#define HEX_CHARS (MAX_MEMHEX_BYTES*2 + 1)
> > > > > +
> > > > > +int trace_seq_putmem_hex(struct trace_seq *s, const void *mem, size_t len)
> > > > > +{
> > > > > + unsigned char hex[HEX_CHARS];
> > > > > + const unsigned char *data = mem;
> > > > > + int i, j;
> > > > > +
> > > > > + if (s->full)
> > > > > + return 0;
> > > >
> > > > What's this ->full thing all about anyway? Some central comment which
> > > > explains the design is needed.
> > >
> > > Comment? What? Git blame isn't good enough for ya? ;-)
> >
> > There's always that. There's also googling for the original list
> > dicsussion. But it's a bit user-unfriendly, particularly when then
> > code has aged was subsequently altered many times.
>
> Although I did not address this because I'm waiting to hear back from
> Johannes Berg, I updated for your other comments. I hope I got them all.
>
> Regardless of this patch series, I pulled out the code from
> trace_output.c and made a separate file for the trace_seq_*() functions
> in kernel/trace/trace_seq.c. I then updated the file with your
> comments. I found a bug or two and I will be dealing with them later as
> this will only be a clean up patch not a bug fix patch.
>
> Anyway, here's the new file:

Would be helpful if I compiled it before posting it :-)

Also, I missed a few EXPORT_SYMBOL_GPL()s along the way.

New update:

-- Steve

/*
* trace_seq.c
*
* Copyright (C) 2008-2014 Red Hat Inc, Steven Rostedt <srostedt@redhat.com>
*
* The trace_seq is a handy tool that allows you to pass a descriptor around
* to a buffer that other functions can write to. It is similar to the
* seq_file functionality but has some differences.
*
* To use it, the trace_seq must be initialized with trace_seq_init().
* This will set up the counters within the descriptor. You can call
* trace_seq_init() more than once to reset the trace_seq to start
* from scratch.
*
* The buffer size is currently PAGE_SIZE, although it may become dynamic
* in the future.
*
* A write to the buffer will either succed or fail. That is, unlike
* sprintf() there will not be a partial write (well it may write into
* the buffer but it wont update the pointers). This allows users to
* try to write something into the trace_seq buffer and if it fails
* they can flush it and try again.
*
*/
#include <linux/uaccess.h>
#include <linux/seq_file.h>
#include <linux/trace_seq.h>

/* How much buffer is left on the trace_seq? */
#define TRACE_SEQ_BUF_LEFT(s) ((PAGE_SIZE - 1) - (s)->len)

/* How much buffer is written? */
#define TRACE_SEQ_BUF_USED(s) min((s)->len, (unsigned int)(PAGE_SIZE - 1))

/**
* trace_print_seq - move the contents of trace_seq into a seq_file
* @m: the seq_file descriptor that is the destination
* @s: the trace_seq descriptor that is the source.
*
* Returns 0 on success and non zero on error. If it succeeds to
* write to the seq_file it will reset the trace_seq, otherwise
* it does not modify the trace_seq to let the caller try again.
*/
int trace_print_seq(struct seq_file *m, struct trace_seq *s)
{
unsigned int len = TRACE_SEQ_BUF_USED(s);
int ret;

ret = seq_write(m, s->buffer, len);

/*
* Only reset this buffer if we successfully wrote to the
* seq_file buffer. This lets the caller try again or
* do something else with the contents.
*/
if (!ret)
trace_seq_init(s);

return ret;
}

/**
* trace_seq_printf - sequence printing of trace information
* @s: trace sequence descriptor
* @fmt: printf format string
*
* The tracer may use either sequence operations or its own
* copy to user routines. To simplify formating of a trace
* trace_seq_printf() is used to store strings into a special
* buffer (@s). Then the output may be either used by
* the sequencer or pulled into another buffer.
*
* Returns 1 if we successfully written all the contents to
* the buffer.
* Returns 0 if we the length to write is bigger than the
* reserved buffer space. In this case, nothing gets written.
*/
int trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
{
unsigned int len = TRACE_SEQ_BUF_LEFT(s);
va_list ap;
int ret;

if (s->full || !len)
return 0;

va_start(ap, fmt);
ret = vsnprintf(s->buffer + s->len, len, fmt, ap);
va_end(ap);

/* If we can't write it all, don't bother writing anything */
if (ret >= len) {
s->full = 1;
return 0;
}

s->len += ret;

return 1;
}
EXPORT_SYMBOL_GPL(trace_seq_printf);

/**
* trace_seq_bitmask - write a bitmask array in its ASCII representation
* @s: trace sequence descriptor
* @maskp: points to an array of unsigned longs that represent a bitmask
* @nmaskbits: The number of bits that are valid in @maskp
*
* Writes a ASCII representation of a bitmask string into @s.
*
* Returns 1 if we successfully written all the contents to
* the buffer.
* Returns 0 if we the length to write is bigger than the
* reserved buffer space. In this case, nothing gets written.
*/
int trace_seq_bitmask(struct trace_seq *s, const unsigned long *maskp,
int nmaskbits)
{
unsigned int len = TRACE_SEQ_BUF_LEFT(s);
int ret;

if (s->full || !len)
return 0;

ret = bitmap_scnprintf(s->buffer, len, maskp, nmaskbits);
s->len += ret;

return 1;
}
EXPORT_SYMBOL_GPL(trace_seq_bitmask);

/**
* trace_seq_vprintf - sequence printing of trace information
* @s: trace sequence descriptor
* @fmt: printf format string
*
* The tracer may use either sequence operations or its own
* copy to user routines. To simplify formating of a trace
* trace_seq_printf is used to store strings into a special
* buffer (@s). Then the output may be either used by
* the sequencer or pulled into another buffer.
*
* Returns 1 if we successfully written all the contents to
* the buffer.
* Returns 0 if we the length to write is bigger than the
* reserved buffer space. In this case, nothing gets written.
*/
int trace_seq_vprintf(struct trace_seq *s, const char *fmt, va_list args)
{
unsigned int len = TRACE_SEQ_BUF_LEFT(s);
int ret;

if (s->full || !len)
return 0;

ret = vsnprintf(s->buffer + s->len, len, fmt, args);

/* If we can't write it all, don't bother writing anything */
if (ret >= len) {
s->full = 1;
return 0;
}

s->len += ret;

return len;
}
EXPORT_SYMBOL_GPL(trace_seq_vprintf);

/**
* trace_seq_bprintf - Write the printf string from binary arguments
* @s: trace sequence descriptor
* @fmt: The format string for the @binary arguments
* @binary: The binary arguments for @fmt.
*
* When recording in a fast path, a printf may be recorded with just
* saving the format and the arguments as they were passed to the
* function, instead of wasting cycles converting the arguments into
* ASCII characters. Instead, the arguments are saved in a 32 bit
* word array that is defined by the format string constraints.
*
* This function will take the format and the binary array and finish
* the conversion into the ASCII string within the buffer.
*
* Returns 1 if we successfully written all the contents to
* the buffer.
* Returns 0 if we the length to write is bigger than the
* reserved buffer space. In this case, nothing gets written.
*/
int trace_seq_bprintf(struct trace_seq *s, const char *fmt, const u32 *binary)
{
unsigned int len = TRACE_SEQ_BUF_LEFT(s);
int ret;

if (s->full || !len)
return 0;

ret = bstr_printf(s->buffer + s->len, len, fmt, binary);

/* If we can't write it all, don't bother writing anything */
if (ret >= len) {
s->full = 1;
return 0;
}

s->len += ret;

return len;
}
EXPORT_SYMBOL_GPL(trace_seq_bprintf);

/**
* trace_seq_puts - trace sequence printing of simple string
* @s: trace sequence descriptor
* @str: simple string to record
*
* The tracer may use either the sequence operations or its own
* copy to user routines. This function records a simple string
* into a special buffer (@s) for later retrieval by a sequencer
* or other mechanism.
*
* Returns 1 if we successfully written all the contents to
* the buffer.
* Returns 0 if we the length to write is bigger than the
* reserved buffer space. In this case, nothing gets written.
*/
int trace_seq_puts(struct trace_seq *s, const char *str)
{
unsigned int len = strlen(str);

if (s->full)
return 0;

if (len > TRACE_SEQ_BUF_LEFT(s)) {
s->full = 1;
return 0;
}

memcpy(s->buffer + s->len, str, len);
s->len += len;

return len;
}
EXPORT_SYMBOL_GPL(trace_seq_puts);

/**
* trace_seq_putc - trace sequence printing of simple character
* @s: trace sequence descriptor
* @c: simple character to record
*
* The tracer may use either the sequence operations or its own
* copy to user routines. This function records a simple charater
* into a special buffer (@s) for later retrieval by a sequencer
* or other mechanism.
*
* Returns 1 if we successfully written all the contents to
* the buffer.
* Returns 0 if we the length to write is bigger than the
* reserved buffer space. In this case, nothing gets written.
*/
int trace_seq_putc(struct trace_seq *s, unsigned char c)
{
if (s->full)
return 0;

if (TRACE_SEQ_BUF_LEFT(s) < 1) {
s->full = 1;
return 0;
}

s->buffer[s->len++] = c;

return 1;
}
EXPORT_SYMBOL_GPL(trace_seq_putc);

/**
* trace_seq_putmem - write raw data into the trace_seq buffer
* @s: trace sequence descriptor
* @mem: The raw memory to copy into the buffer
* @len: The length of the raw memory to copy (in bytes)
*
* There may be cases where raw memory needs to be written into the
* buffer and a strcpy() would not work. Using this function allows
* for such cases.
*
* Returns 1 if we successfully written all the contents to
* the buffer.
* Returns 0 if we the length to write is bigger than the
* reserved buffer space. In this case, nothing gets written.
*/
int trace_seq_putmem(struct trace_seq *s, const void *mem, unsigned int len)
{
if (s->full)
return 0;

if (len > TRACE_SEQ_BUF_LEFT(s)) {
s->full = 1;
return 0;
}

memcpy(s->buffer + s->len, mem, len);
s->len += len;

return len;
}
EXPORT_SYMBOL_GPL(trace_seq_putmem);

#define HEX_CHARS (MAX_MEMHEX_BYTES*2 + 1)

/**
* trace_seq_putmem_hex - write raw memory into the buffer in ASCII hex
* @s: trace sequence descriptor
* @mem: The raw memory to write its hex ASCII representation of
* @len: The length of the raw memory to copy (in bytes)
*
* This is similar to trace_seq_putmem() except instead of just copying the
* raw memory into the buffer it writes its ASCII representation of it
* in hex characters.
*
* Returns 1 if we successfully written all the contents to
* the buffer.
* Returns 0 if we the length to write is bigger than the
* reserved buffer space. In this case, nothing gets written.
*/
int trace_seq_putmem_hex(struct trace_seq *s, const void *mem,
unsigned int len)
{
unsigned char hex[HEX_CHARS];
const unsigned char *data = mem;
int i, j;

if (s->full)
return 0;

#ifdef __BIG_ENDIAN
for (i = 0, j = 0; i < len; i++) {
#else
for (i = len-1, j = 0; i >= 0; i--) {
#endif
hex[j++] = hex_asc_hi(data[i]);
hex[j++] = hex_asc_lo(data[i]);
}
hex[j++] = ' ';

return trace_seq_putmem(s, hex, j);
}
EXPORT_SYMBOL_GPL(trace_seq_putmem_hex);

/**
* trace_seq_reserve - reserve space on the sequence buffer
* @s: trace sequence descriptor
* @len: The amount to reserver.
*
* If for some reason there is a need to save some space on the
* buffer to fill in later, this function is used for that purpose.
* The given length will be reserved and the pointer to that
* location on the buffer is returned, unless there is not enough
* buffer left to hold the given length then NULL is returned.
*/
void *trace_seq_reserve(struct trace_seq *s, unsigned int len)
{
void *ret;

if (s->full)
return NULL;

if (len > TRACE_SEQ_BUF_LEFT(s)) {
s->full = 1;
return NULL;
}

ret = s->buffer + s->len;
s->len += len;

return ret;
}
EXPORT_SYMBOL_GPL(trace_seq_reserve);

/**
* trace_seq_path - copy a path into the sequence buffer
* @s: trace sequence descriptor
* @path: path to write into the sequence buffer.
*
* Write a path name into the sequence buffer.
*
* Returns 1 if we successfully written all the contents to
* the buffer.
* Returns 0 if we the length to write is bigger than the
* reserved buffer space. In this case, nothing gets written.
*/
int trace_seq_path(struct trace_seq *s, const struct path *path)
{
unsigned char *p;

if (s->full)
return 0;

if (TRACE_SEQ_BUF_LEFT(s) < 1) {
s->full = 1;
return 0;
}

p = d_path(path, s->buffer + s->len, PAGE_SIZE - s->len);
if (!IS_ERR(p)) {
p = mangle_path(s->buffer + s->len, p, "\n");
if (p) {
s->len = p - s->buffer;
return 1;
}
} else {
s->buffer[s->len++] = '?';
return 1;
}

s->full = 1;
return 0;
}
EXPORT_SYMBOL_GPL(trace_seq_path);

/**
* trace_seq_to_user - copy the squence buffer to user space
* @s: trace sequence descriptor
* @ubuf: The userspace memory location to copy to
* @cnt: The amount to copy
*
* Copies the sequence buffer into the userspace memory pointed to
* by @ubuf. It starts from the last read position (@s->readpos)
* and writes up to @cnt characters or till it reaches the end of
* the content in the buffer (@s->len), which ever comes first.
*
* On success, it returns a positive number of the number of bytes
* it copied.
*
* On failure it returns -EBUSY if all of the content in the
* sequence has been already read, which includes nothing in the
* sequenc (@s->len == @s->readpos).
*
* Returns -EFAULT if the copy to userspace fails.
*/
int trace_seq_to_user(struct trace_seq *s, char __user *ubuf, int cnt)
{
int len;
int ret;

if (!cnt)
return 0;

if (s->len <= s->readpos)
return -EBUSY;

len = s->len - s->readpos;
if (cnt > len)
cnt = len;
ret = copy_to_user(ubuf, s->buffer + s->readpos, cnt);
if (ret == cnt)
return -EFAULT;

cnt -= ret;

s->readpos += cnt;
return cnt;
}
EXPORT_SYMBOL_GPL(trace_seq_to_user);