Add generic mmap funcion to read page from cpu data

This patch adds a generic mmap page reading that simply
swaps the old mmap with a new mapping. This avoids needing to use
get_next_page in an awkward and error prone fashion.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 74 insertions, 34 deletions

diff --git a/trace-input.c b/trace-input.c
index 46c5e05..cacc136 100644
--- a/trace-input.c
+++ b/trace-input.c
@@ -18,6 +18,8 @@
 
 #include "trace-cmd.h"
 
+/* for debugging read instead of mmap */
+static int force_read = 0;
 
 struct cpu_data {
         /* the first two never change */
@@ -28,6 +30,7 @@ struct cpu_data {
         unsigned long long      timestamp;
         struct record           *next;
         char                    *page;
+        void                    *read_page;
         int                     cpu;
         int                     index;
         int                     page_size;
@@ -493,47 +496,83 @@ static int calc_index(struct tracecmd_input *handle,
 static void
 update_cpu_data_index(struct tracecmd_input *handle, int cpu)
 {
-        handle->cpu_data[cpu].offset += handle->page_size;
         handle->cpu_data[cpu].size -= handle->page_size;
         handle->cpu_data[cpu].index = 0;
 }
 
-static int get_next_page(struct tracecmd_input *handle, int cpu)
+static void free_page(struct tracecmd_input *handle, int cpu)
+{
+        if (!handle->cpu_data[cpu].page)
+                return;
+
+        if (handle->read_page) {
+                handle->cpu_data[cpu].page = NULL;
+                return;
+        }
+                
+        munmap(handle->cpu_data[cpu].page, handle->page_size);
+        handle->cpu_data[cpu].page = NULL;
+}
+
+static int get_read_page(struct tracecmd_input *handle, int cpu,
+                         off64_t offset)
 {
         off64_t save_seek;
         off64_t ret;
 
-        if (!handle->cpu_data[cpu].page)
-                return 0;
+        free_page(handle, cpu);
 
-        if (handle->read_page) {
-                if (handle->cpu_data[cpu].size <= handle->page_size) {
-                        free(handle->cpu_data[cpu].page);
-                        handle->cpu_data[cpu].page = NULL;
-                        handle->cpu_data[cpu].offset = 0;
-                        return 0;
-                }
+        handle->cpu_data[cpu].page = handle->cpu_data[cpu].read_page;
 
-                update_cpu_data_index(handle, cpu);
+        /* other parts of the code may expect the pointer to not move */
+        save_seek = lseek64(handle->fd, 0, SEEK_CUR);
 
-                /* other parts of the code may expect the pointer to not move */
-                save_seek = lseek64(handle->fd, 0, SEEK_CUR);
+        ret = lseek64(handle->fd, offset, SEEK_SET);
+        if (ret < 0)
+                return -1;
+        ret = read(handle->fd, handle->cpu_data[cpu].page, handle->page_size);
+        if (ret < 0)
+                return -1;
 
-                ret = lseek64(handle->fd, handle->cpu_data[cpu].offset, SEEK_SET);
-                if (ret < 0)
-                        return -1;
-                ret = read(handle->fd, handle->cpu_data[cpu].page, handle->page_size);
-                if (ret < 0)
-                        return -1;
+        /* reset the file pointer back */
+        lseek64(handle->fd, save_seek, SEEK_SET);
+
+        return 0;
 
-                /* reset the file pointer back */
-                lseek64(handle->fd, save_seek, SEEK_SET);
+}
 
-                return 0;
+static int get_page(struct tracecmd_input *handle, int cpu,
+                    off64_t offset)
+{
+        if (offset & (handle->page_size - 1)) {
+                errno = -EINVAL;
+                die("bad page offset %llx", offset);
+                return -1;
         }
 
-        munmap(handle->cpu_data[cpu].page, handle->page_size);
-        handle->cpu_data[cpu].page = NULL;
+        if (handle->read_page)
+                return get_read_page(handle, cpu, offset);
+
+        if (handle->cpu_data[cpu].page)
+                free_page(handle, cpu);
+
+        handle->cpu_data[cpu].offset = offset;
+        
+        handle->cpu_data[cpu].page = mmap(NULL, handle->page_size, PROT_READ, MAP_PRIVATE,
+                                          handle->fd, offset);
+        if (handle->cpu_data[cpu].page == MAP_FAILED)
+                return -1;
+
+        return 0;
+}
+static int get_next_page(struct tracecmd_input *handle, int cpu)
+{
+        off64_t offset;
+
+        if (!handle->cpu_data[cpu].page)
+                return 0;
+
+        free_page(handle, cpu);
 
         if (handle->cpu_data[cpu].size <= handle->page_size) {
                 handle->cpu_data[cpu].offset = 0;
@@ -542,12 +581,9 @@ static int get_next_page(struct tracecmd_input *handle, int cpu)
 
         update_cpu_data_index(handle, cpu);
         
-        handle->cpu_data[cpu].page = mmap(NULL, handle->page_size, PROT_READ, MAP_PRIVATE,
-                                  handle->fd, handle->cpu_data[cpu].offset);
-        if (handle->cpu_data[cpu].page == MAP_FAILED)
-                return -1;
+        offset = handle->cpu_data[cpu].offset + handle->page_size;
 
-        return 0;
+        return get_page(handle, cpu, offset);
 }
 
 enum old_ring_buffer_type {
@@ -946,10 +982,12 @@ static int init_read(struct tracecmd_input *handle, int cpu)
         off64_t ret;
         off64_t save_seek;
 
-        handle->cpu_data[cpu].page = malloc(handle->page_size);
-        if (!handle->cpu_data[cpu].page)
+        handle->cpu_data[cpu].read_page = malloc(handle->page_size);
+        if (!handle->cpu_data[cpu].read_page)
                 return -1;
 
+        handle->cpu_data[cpu].page = handle->cpu_data[cpu].read_page;
+
         /* other parts of the code may expect the pointer to not move */
         save_seek = lseek64(handle->fd, 0, SEEK_CUR);
 
@@ -976,9 +1014,11 @@ static int init_cpu(struct tracecmd_input *handle, int cpu)
         if (handle->read_page)
                 return init_read(handle, cpu);
 
-        handle->cpu_data[cpu].page = mmap(NULL, handle->page_size, PROT_READ,
+        if (!force_read) {
+                handle->cpu_data[cpu].page = mmap(NULL, handle->page_size, PROT_READ,
                                   MAP_PRIVATE, handle->fd, handle->cpu_data[cpu].offset);
-        if (handle->cpu_data[cpu].page == MAP_FAILED) {
+        }
+        if (force_read || handle->cpu_data[cpu].page == MAP_FAILED) {
                 /* fall back to just reading pages */
                 perror("mmap");
                 fprintf(stderr, "Can not mmap file, will read instead\n");