From 9a38a8856f41f90cc7e57798c544e3fe77033196 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Red Hat)" Date: Wed, 30 Sep 2015 11:11:15 -0400 Subject: tracing: Add a method to pass in trace_array descriptor to option files In preparation of having the multi buffer instances having their own trace option flags, the trace option files needs a way to not only pass in the flag they represent, but also the trace_array descriptor. A new field is added to the trace_array descriptor called trace_flags_index, which is a 32 byte character array representing a bit. This array is simply filled with the index of the array, where index_array[n] = n; Then the address of this array is passed to the file callbacks instead of the index of the flag index. Then to retrieve both the flag index and the trace_array descriptor: data is the passed in argument. index = *(unsigned char *)data; data -= index; /* Now data points to the address of the array in the trace_array */ tr = container_of(data, struct trace_array, trace_flags_index); Suggested-by: Johannes Berg Signed-off-by: Steven Rostedt diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 4e82f4a..5f48188 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6186,14 +6186,51 @@ static const struct file_operations trace_options_fops = { .llseek = generic_file_llseek, }; +/* + * In order to pass in both the trace_array descriptor as well as the index + * to the flag that the trace option file represents, the trace_array + * has a character array of trace_flags_index[], which holds the index + * of the bit for the flag it represents. index[0] == 0, index[1] == 1, etc. + * The address of this character array is passed to the flag option file + * read/write callbacks. + * + * In order to extract both the index and the trace_array descriptor, + * get_tr_index() uses the following algorithm. + * + * idx = *ptr; + * + * As the pointer itself contains the address of the index (remember + * index[1] == 1). + * + * Then to get the trace_array descriptor, by subtracting that index + * from the ptr, we get to the start of the index itself. + * + * ptr - idx == &index[0] + * + * Then a simple container_of() from that pointer gets us to the + * trace_array descriptor. + */ +static void get_tr_index(void *data, struct trace_array **ptr, + unsigned int *pindex) +{ + *pindex = *(unsigned char *)data; + + *ptr = container_of(data - *pindex, struct trace_array, + trace_flags_index); +} + static ssize_t trace_options_core_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos) { - long index = (long)filp->private_data; + void *tr_index = filp->private_data; + struct trace_array *tr; + unsigned int index; char *buf; - if (global_trace.trace_flags & (1 << index)) + get_tr_index(tr_index, &tr, &index); + + if (tr->trace_flags & (1 << index)) buf = "1\n"; else buf = "0\n"; @@ -6205,11 +6242,14 @@ static ssize_t trace_options_core_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos) { - struct trace_array *tr = &global_trace; - long index = (long)filp->private_data; + void *tr_index = filp->private_data; + struct trace_array *tr; + unsigned int index; unsigned long val; int ret; + get_tr_index(tr_index, &tr, &index); + ret = kstrtoul_from_user(ubuf, cnt, 10, &val); if (ret) return ret; @@ -6339,8 +6379,9 @@ create_trace_option_core_file(struct trace_array *tr, if (!t_options) return NULL; - return trace_create_file(option, 0644, t_options, (void *)index, - &trace_options_core_fops); + return trace_create_file(option, 0644, t_options, + (void *)&tr->trace_flags_index[index], + &trace_options_core_fops); } static __init void create_trace_options_dir(struct trace_array *tr) @@ -6490,6 +6531,15 @@ static void free_trace_buffers(struct trace_array *tr) #endif } +static void init_trace_flags_index(struct trace_array *tr) +{ + int i; + + /* Used by the trace options files */ + for (i = 0; i < TRACE_FLAGS_MAX_SIZE; i++) + tr->trace_flags_index[i] = i; +} + static int instance_mkdir(const char *name) { struct trace_array *tr; @@ -6542,6 +6592,7 @@ static int instance_mkdir(const char *name) } init_tracer_tracefs(tr, tr->dir); + init_trace_flags_index(tr); list_add(&tr->list, &ftrace_trace_arrays); @@ -7068,7 +7119,7 @@ __init static int tracer_alloc_buffers(void) * Make sure we don't accidently add more trace options * than we have bits for. */ - BUILD_BUG_ON(TRACE_ITER_LAST_BIT > 32); + BUILD_BUG_ON(TRACE_ITER_LAST_BIT > TRACE_FLAGS_MAX_SIZE); if (!alloc_cpumask_var(&tracing_buffer_mask, GFP_KERNEL)) goto out; @@ -7128,6 +7179,8 @@ __init static int tracer_alloc_buffers(void) ftrace_init_global_array_ops(&global_trace); + init_trace_flags_index(&global_trace); + register_tracer(&nop_trace); /* All seems OK, enable tracing */ diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index eda4e6f..423cb48 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -168,6 +168,8 @@ struct trace_buffer { int cpu; }; +#define TRACE_FLAGS_MAX_SIZE 32 + /* * The trace array - an array of per-CPU trace arrays. This is the * highest level data structure that individual tracers deal with. @@ -218,6 +220,7 @@ struct trace_array { int clock_id; struct tracer *current_trace; unsigned int trace_flags; + unsigned char trace_flags_index[TRACE_FLAGS_MAX_SIZE]; unsigned int flags; raw_spinlock_t start_lock; struct dentry *dir; -- cgit v0.10.2