[PATCH 1/4] printk: ringbuffer: support dataless records
From: John Ogness
Date: Fri Jul 17 2020 - 19:49:03 EST
In order to support storage of continuous lines, dataless records must
be allowed. For example, these are generated with the legal calls:
pr_info("");
pr_cont("\n");
Currently dataless records are denoted by INVALID_LPOS in order to
recognize failed prb_reserve() calls. Change the code to use two
different identifiers (FAILED_LPOS and NO_LPOS) to distinguish
between failed prb_reserve() records and successful dataless records.
Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
---
kernel/printk/printk_ringbuffer.c | 58 ++++++++++++++-----------------
kernel/printk/printk_ringbuffer.h | 15 ++++----
2 files changed, 35 insertions(+), 38 deletions(-)
diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
index 7355ca99e852..54b0a6324dbf 100644
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -264,6 +264,9 @@
/* Determine how many times the data array has wrapped. */
#define DATA_WRAPS(data_ring, lpos) ((lpos) >> (data_ring)->size_bits)
+/* Determine if a logical position refers to a data-less block. */
+#define LPOS_DATALESS(lpos) ((lpos) & 1UL)
+
/* Get the logical position at index 0 of the current wrap. */
#define DATA_THIS_WRAP_START_LPOS(data_ring, lpos) \
((lpos) & ~DATA_SIZE_MASK(data_ring))
@@ -320,21 +323,13 @@ static unsigned int to_blk_size(unsigned int size)
* block does not exceed the maximum possible size that could fit within the
* ringbuffer. This function provides that basic size check so that the
* assumption is safe.
- *
- * Writers are also not allowed to write 0-sized (data-less) records. Such
- * records are used only internally by the ringbuffer.
*/
static bool data_check_size(struct prb_data_ring *data_ring, unsigned int size)
{
struct prb_data_block *db = NULL;
- /*
- * Writers are not allowed to write data-less records. Such records
- * are used only internally by the ringbuffer to denote records where
- * their data failed to allocate or have been lost.
- */
if (size == 0)
- return false;
+ return true;
/*
* Ensure the alignment padded size could possibly fit in the data
@@ -568,8 +563,8 @@ static bool data_push_tail(struct printk_ringbuffer *rb,
unsigned long tail_lpos;
unsigned long next_lpos;
- /* If @lpos is not valid, there is nothing to do. */
- if (lpos == INVALID_LPOS)
+ /* If @lpos is from a data-less block, there is nothing to do. */
+ if (LPOS_DATALESS(lpos))
return true;
/*
@@ -962,8 +957,8 @@ static char *data_alloc(struct printk_ringbuffer *rb,
if (size == 0) {
/* Specify a data-less block. */
- blk_lpos->begin = INVALID_LPOS;
- blk_lpos->next = INVALID_LPOS;
+ blk_lpos->begin = NO_LPOS;
+ blk_lpos->next = NO_LPOS;
return NULL;
}
@@ -976,8 +971,8 @@ static char *data_alloc(struct printk_ringbuffer *rb,
if (!data_push_tail(rb, data_ring, next_lpos - DATA_SIZE(data_ring))) {
/* Failed to allocate, specify a data-less block. */
- blk_lpos->begin = INVALID_LPOS;
- blk_lpos->next = INVALID_LPOS;
+ blk_lpos->begin = FAILED_LPOS;
+ blk_lpos->next = FAILED_LPOS;
return NULL;
}
@@ -1025,6 +1020,10 @@ static char *data_alloc(struct printk_ringbuffer *rb,
static unsigned int space_used(struct prb_data_ring *data_ring,
struct prb_data_blk_lpos *blk_lpos)
{
+ /* Data-less blocks take no space. */
+ if (LPOS_DATALESS(blk_lpos->begin))
+ return 0;
+
if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next)) {
/* Data block does not wrap. */
return (DATA_INDEX(data_ring, blk_lpos->next) -
@@ -1080,11 +1079,8 @@ bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
if (!data_check_size(&rb->text_data_ring, r->text_buf_size))
goto fail;
- /* Records are allowed to not have dictionaries. */
- if (r->dict_buf_size) {
- if (!data_check_size(&rb->dict_data_ring, r->dict_buf_size))
- goto fail;
- }
+ if (!data_check_size(&rb->dict_data_ring, r->dict_buf_size))
+ goto fail;
/*
* Descriptors in the reserved state act as blockers to all further
@@ -1212,10 +1208,8 @@ static char *get_data(struct prb_data_ring *data_ring,
struct prb_data_block *db;
/* Data-less data block description. */
- if (blk_lpos->begin == INVALID_LPOS &&
- blk_lpos->next == INVALID_LPOS) {
+ if (LPOS_DATALESS(blk_lpos->begin) && LPOS_DATALESS(blk_lpos->next))
return NULL;
- }
/* Regular data block: @begin less than @next and in same wrap. */
if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next) &&
@@ -1355,11 +1349,11 @@ static int desc_read_committed_seq(struct prb_desc_ring *desc_ring,
/*
* A descriptor in the reusable state may no longer have its data
- * available; report it as a data-less record. Or the record may
- * actually be a data-less record.
+ * available; report it as existing but with lost data. Or the record
+ * may actually be a record with lost data.
*/
if (d_state == desc_reusable ||
- (blk_lpos->begin == INVALID_LPOS && blk_lpos->next == INVALID_LPOS)) {
+ (blk_lpos->begin == FAILED_LPOS && blk_lpos->next == FAILED_LPOS)) {
return -ENOENT;
}
@@ -1402,7 +1396,9 @@ static int prb_read(struct printk_ringbuffer *rb, u64 seq,
/* Copy text data. If it fails, this is a data-less record. */
if (!copy_data(&rb->text_data_ring, &desc.text_blk_lpos, desc.info.text_len,
r->text_buf, r->text_buf_size, line_count)) {
- return -ENOENT;
+ /* Report an error if there should have been data. */
+ if (desc.info.text_len != 0)
+ return -ENOENT;
}
/*
@@ -1659,10 +1655,10 @@ void prb_init(struct printk_ringbuffer *rb,
descs[_DESCS_COUNT(descbits) - 1].info.seq = 0;
atomic_long_set(&(descs[_DESCS_COUNT(descbits) - 1].state_var), DESC0_SV(descbits));
- descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.begin = INVALID_LPOS;
- descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.next = INVALID_LPOS;
- descs[_DESCS_COUNT(descbits) - 1].dict_blk_lpos.begin = INVALID_LPOS;
- descs[_DESCS_COUNT(descbits) - 1].dict_blk_lpos.next = INVALID_LPOS;
+ descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.begin = FAILED_LPOS;
+ descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.next = FAILED_LPOS;
+ descs[_DESCS_COUNT(descbits) - 1].dict_blk_lpos.begin = FAILED_LPOS;
+ descs[_DESCS_COUNT(descbits) - 1].dict_blk_lpos.next = FAILED_LPOS;
}
/**
diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h
index 3e46a7423c13..e6302da041f9 100644
--- a/kernel/printk/printk_ringbuffer.h
+++ b/kernel/printk/printk_ringbuffer.h
@@ -120,12 +120,13 @@ struct prb_reserved_entry {
#define DESC_FLAGS_MASK (DESC_COMMITTED_MASK | DESC_REUSE_MASK)
#define DESC_ID_MASK (~DESC_FLAGS_MASK)
#define DESC_ID(sv) ((sv) & DESC_ID_MASK)
-#define INVALID_LPOS 1
+#define FAILED_LPOS 0x1
+#define NO_LPOS 0x3
-#define INVALID_BLK_LPOS \
+#define FAILED_BLK_LPOS \
{ \
- .begin = INVALID_LPOS, \
- .next = INVALID_LPOS, \
+ .begin = FAILED_LPOS, \
+ .next = FAILED_LPOS, \
}
/*
@@ -147,7 +148,7 @@ struct prb_reserved_entry {
*
* To satisfy Req1, the tail initially points to a descriptor that is
* minimally initialized (having no data block, i.e. data-less with the
- * data block's lpos @begin and @next values set to INVALID_LPOS).
+ * data block's lpos @begin and @next values set to FAILED_LPOS).
*
* To satisfy Req2, the initial tail descriptor is initialized to the
* reusable state. Readers recognize reusable descriptors as existing
@@ -242,8 +243,8 @@ static struct prb_desc _##name##_descs[_DESCS_COUNT(descbits)] = { \
/* reusable */ \
.state_var = ATOMIC_INIT(DESC0_SV(descbits)), \
/* no associated data block */ \
- .text_blk_lpos = INVALID_BLK_LPOS, \
- .dict_blk_lpos = INVALID_BLK_LPOS, \
+ .text_blk_lpos = FAILED_BLK_LPOS, \
+ .dict_blk_lpos = FAILED_BLK_LPOS, \
}, \
}; \
static struct printk_ringbuffer name = { \
--
2.20.1