pstore/ram: Factor ramoops_get_next_prz() out of ramoops_pstore_read()

This will help make code clearer when we'll add support for other
message types.

The patch also changes return value from -EINVAL to 0 in case of
end-of-records. The exact value doesn't matter for pstore (it should
be just <= 0), but 0 feels more correct.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 32 insertions, 9 deletions

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 6b7676738493..d770d7266e96 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -85,6 +85,33 @@ static int ramoops_pstore_open(struct pstore_info *psi)
         return 0;
 }
 
+static struct persistent_ram_zone *
+ramoops_get_next_prz(struct persistent_ram_zone *przs[], uint *c, uint max,
+                     u64 *id,
+                     enum pstore_type_id *typep, enum pstore_type_id type,
+                     bool update)
+{
+        struct persistent_ram_zone *prz;
+        int i = (*c)++;
+
+        if (i >= max)
+                return NULL;
+
+        prz = przs[i];
+
+        if (update) {
+                /* Update old/shadowed buffer. */
+                persistent_ram_save_old(prz);
+                if (!persistent_ram_old_size(prz))
+                        return NULL;
+        }
+
+        *typep = type;
+        *id = i;
+
+        return prz;
+}
+
 static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
                                    struct timespec *time,
                                    char **buf,
@@ -94,20 +121,16 @@ static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
         struct ramoops_context *cxt = psi->data;
         struct persistent_ram_zone *prz;
 
-        if (cxt->dump_read_cnt >= cxt->max_dump_cnt)
-                return -EINVAL;
-
-        *id = cxt->dump_read_cnt++;
-        prz = cxt->przs[*id];
+        prz = ramoops_get_next_prz(cxt->przs, &cxt->dump_read_cnt,
+                                   cxt->max_dump_cnt, id, type,
+                                   PSTORE_TYPE_DMESG, 1);
+        if (!prz)
+                return 0;
 
-        /* Only supports dmesg output so far. */
-        *type = PSTORE_TYPE_DMESG;
         /* TODO(kees): Bogus time for the moment. */
         time->tv_sec = 0;
         time->tv_nsec = 0;
 
-        /* Update old/shadowed buffer. */
-        persistent_ram_save_old(prz);
         size = persistent_ram_old_size(prz);
         *buf = kmalloc(size, GFP_KERNEL);
         if (*buf == NULL)