/* SPDX-License-Identifier: GPL-2.0 */ #ifndef _KERNEL_PRINTK_RINGBUFFER_H #define _KERNEL_PRINTK_RINGBUFFER_H #include <linux/atomic.h> #include <linux/bits.h> #include <linux/dev_printk.h> #include <linux/stddef.h> #include <linux/types.h> /* * Meta information about each stored message. * * All fields are set by the printk code except for @seq, which is * set by the ringbuffer code. */ struct printk_info { u64 seq; /* sequence number */ u64 ts_nsec; /* timestamp in nanoseconds */ u16 text_len; /* length of text message */ u8 facility; /* syslog facility */ u8 flags:5; /* internal record flags */ u8 level:3; /* syslog level */ u32 caller_id; /* thread id or processor id */ #ifdef CONFIG_PRINTK_EXECUTION_CTX u32 caller_id2; /* caller_id complement */ /* name of the task that generated the message */ char comm[TASK_COMM_LEN]; #endif struct dev_printk_info dev_info; }; /* * A structure providing the buffers, used by writers and readers. * * Writers: * Using prb_rec_init_wr(), a writer sets @text_buf_size before calling * prb_reserve(). On success, prb_reserve() sets @info and @text_buf to * buffers reserved for that writer. * * Readers: * Using prb_rec_init_rd(), a reader sets all fields before calling * prb_read_valid(). Note that the reader provides the @info and @text_buf, * buffers. On success, the struct pointed to by @info will be filled and * the char array pointed to by @text_buf will be filled with text data. */ struct printk_record { struct printk_info *info; char *text_buf; unsigned int text_buf_size; }; /* Specifies the logical position and span of a data block. */ struct prb_data_blk_lpos { unsigned long begin; unsigned long next; }; /* * A descriptor: the complete meta-data for a record. * * @state_var: A bitwise combination of descriptor ID and descriptor state. */ struct prb_desc { atomic_long_t state_var; struct prb_data_blk_lpos text_blk_lpos; }; /* A ringbuffer of "ID + data" elements. */ struct prb_data_ring { unsigned int size_bits; char *data; atomic_long_t head_lpos; atomic_long_t tail_lpos; }; /* A ringbuffer of "struct prb_desc" elements. */ struct prb_desc_ring { unsigned int count_bits; struct prb_desc *descs; struct printk_info *infos; atomic_long_t head_id; atomic_long_t tail_id; atomic_long_t last_finalized_seq; }; /* * The high level structure representing the printk ringbuffer. * * @fail: Count of failed prb_reserve() calls where not even a data-less * record was created. */ struct printk_ringbuffer { struct prb_desc_ring desc_ring; struct prb_data_ring text_data_ring; atomic_long_t fail; }; /* * Used by writers as a reserve/commit handle. * * @rb: Ringbuffer where the entry is reserved. * @irqflags: Saved irq flags to restore on entry commit. * @id: ID of the reserved descriptor. * @text_space: Total occupied buffer space in the text data ring, including * ID, alignment padding, and wrapping data blocks. * * This structure is an opaque handle for writers. Its contents are only * to be used by the ringbuffer implementation. */ struct prb_reserved_entry { struct printk_ringbuffer *rb; unsigned long irqflags; unsigned long id; unsigned int text_space; }; /* The possible responses of a descriptor state-query. */ enum desc_state { desc_miss = -1, /* ID mismatch (pseudo state) */ desc_reserved = 0x0, /* reserved, in use by writer */ desc_committed = 0x1, /* committed by writer, could get reopened */ desc_finalized = 0x2, /* committed, no further modification allowed */ desc_reusable = 0x3, /* free, not yet used by any writer */ }; #define _DATA_SIZE(sz_bits) (1UL << (sz_bits)) #define _DESCS_COUNT(ct_bits) (1U << (ct_bits)) #define DESC_SV_BITS BITS_PER_LONG #define DESC_FLAGS_SHIFT (DESC_SV_BITS - 2) #define DESC_FLAGS_MASK (3UL << DESC_FLAGS_SHIFT) #define DESC_STATE(sv) (3UL & (sv >> DESC_FLAGS_SHIFT)) #define DESC_SV(id, state) (((unsigned long)state << DESC_FLAGS_SHIFT) | id) #define DESC_ID_MASK (~DESC_FLAGS_MASK) #define DESC_ID(sv) ((sv) & DESC_ID_MASK) /* * Special data block logical position values (for fields of * @prb_desc.text_blk_lpos). * * - Bit0 is used to identify if the record has no data block. (Implemented in * the LPOS_DATALESS() macro.) * * - Bit1 specifies the reason for not having a data block. * * These special values could never be real lpos values because of the * meta data and alignment padding of data blocks. (See to_blk_size() for * details.) */ #define FAILED_LPOS 0x1 #define EMPTY_LINE_LPOS 0x3 #define FAILED_BLK_LPOS \ { \ .begin = FAILED_LPOS, \ .next = FAILED_LPOS, \ } /* * Descriptor Bootstrap * * The descriptor array is minimally initialized to allow immediate usage * by readers and writers. The requirements that the descriptor array * initialization must satisfy: * * Req1 * The tail must point to an existing (committed or reusable) descriptor. * This is required by the implementation of prb_first_seq(). * * Req2 * Readers must see that the ringbuffer is initially empty. * * Req3 * The first record reserved by a writer is assigned sequence number 0. * * 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 FAILED_LPOS). * * To satisfy Req2, the initial tail descriptor is initialized to the * reusable state. Readers recognize reusable descriptors as existing * records, but skip over them. * * To satisfy Req3, the last descriptor in the array is used as the initial * head (and tail) descriptor. This allows the first record reserved by a * writer (head + 1) to be the first descriptor in the array. (Only the first * descriptor in the array could have a valid sequence number of 0.) * * The first time a descriptor is reserved, it is assigned a sequence number * with the value of the array index. A "first time reserved" descriptor can * be recognized because it has a sequence number of 0 but does not have an * index of 0. (Only the first descriptor in the array could have a valid * sequence number of 0.) After the first reservation, all future reservations * (recycling) simply involve incrementing the sequence number by the array * count. * * Hack #1 * Only the first descriptor in the array is allowed to have the sequence * number 0. In this case it is not possible to recognize if it is being * reserved the first time (set to index value) or has been reserved * previously (increment by the array count). This is handled by _always_ * incrementing the sequence number by the array count when reserving the * first descriptor in the array. In order to satisfy Req3, the sequence * number of the first descriptor in the array is initialized to minus * the array count. Then, upon the first reservation, it is incremented * to 0, thus satisfying Req3. * * Hack #2 * prb_first_seq() can be called at any time by readers to retrieve the * sequence number of the tail descriptor. However, due to Req2 and Req3, * initially there are no records to report the sequence number of * (sequence numbers are u64 and there is nothing less than 0). To handle * this, the sequence number of the initial tail descriptor is initialized * to 0. Technically this is incorrect, because there is no record with * sequence number 0 (yet) and the tail descriptor is not the first * descriptor in the array. But it allows prb_read_valid() to correctly * report the existence of a record for _any_ given sequence number at all * times. Bootstrapping is complete when the tail is pushed the first * time, thus finally pointing to the first descriptor reserved by a * writer, which has the assigned sequence number 0. */ /* * Initiating Logical Value Overflows * * Both logical position (lpos) and ID values can be mapped to array indexes * but may experience overflows during the lifetime of the system. To ensure * that printk_ringbuffer can handle the overflows for these types, initial * values are chosen that map to the correct initial array indexes, but will * result in overflows soon. * * BLK0_LPOS * The initial @head_lpos and @tail_lpos for data rings. It is at index * 0 and the lpos value is such that it will overflow on the first wrap. * * DESC0_ID * The initial @head_id and @tail_id for the desc ring. It is at the last * index of the descriptor array (see Req3 above) and the ID value is such * that it will overflow on the second wrap. */ #define BLK0_LPOS(sz_bits) (-(_DATA_SIZE(sz_bits))) #define DESC0_ID(ct_bits) DESC_ID(-(_DESCS_COUNT(ct_bits) + 1)) #define DESC0_SV(ct_bits) DESC_SV(DESC0_ID(ct_bits), desc_reusable) /* * Define a ringbuffer with an external text data buffer. The same as * DEFINE_PRINTKRB() but requires specifying an external buffer for the * text data. * * Note: The specified external buffer must be of the size: * 2 ^ (descbits + avgtextbits) */ #define _DEFINE_PRINTKRB(name, descbits, avgtextbits, text_buf) \ static struct prb_desc _##name##_descs[_DESCS_COUNT(descbits)] = { \ /* the initial head and tail */ \ [_DESCS_COUNT(descbits) - 1] = { \ /* reusable */ \ .state_var = ATOMIC_INIT(DESC0_SV(descbits)), \ /* no associated data block */ \ .text_blk_lpos = FAILED_BLK_LPOS, \ }, \ }; \ static struct printk_info _##name##_infos[_DESCS_COUNT(descbits)] = { \ /* this will be the first record reserved by a writer */ \ [0] = { \ /* will be incremented to 0 on the first reservation */ \ .seq = -(u64)_DESCS_COUNT(descbits), \ }, \ /* the initial head and tail */ \ [_DESCS_COUNT(descbits) - 1] = { \ /* reports the first seq value during the bootstrap phase */ \ .seq = 0, \ }, \ }; \ static struct printk_ringbuffer name = { \ .desc_ring = { \ .count_bits = descbits, \ .descs = &_##name##_descs[0], \ .infos = &_##name##_infos[0], \ .head_id = ATOMIC_INIT(DESC0_ID(descbits)), \ .tail_id = ATOMIC_INIT(DESC0_ID(descbits)), \ .last_finalized_seq = ATOMIC_INIT(0), \ }, \ .text_data_ring = { \ .size_bits = (avgtextbits) + (descbits), \ .data = text_buf, \ .head_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \ .tail_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \ }, \ .fail = ATOMIC_LONG_INIT(0), \ } /** * DEFINE_PRINTKRB() - Define a ringbuffer. * * @name: The name of the ringbuffer variable. * @descbits: The number of descriptors as a power-of-2 value. * @avgtextbits: The average text data size per record as a power-of-2 value. * * This is a macro for defining a ringbuffer and all internal structures * such that it is ready for immediate use. See _DEFINE_PRINTKRB() for a * variant where the text data buffer can be specified externally. */ #define DEFINE_PRINTKRB(name, descbits, avgtextbits) \ static char _##name##_text[1U << ((avgtextbits) + (descbits))] \ __aligned(__alignof__(unsigned long)); \ _DEFINE_PRINTKRB(name, descbits, avgtextbits, &_##name##_text[0]) /* Writer Interface */ /** * prb_rec_init_wr() - Initialize a buffer for writing records. * * @r: The record to initialize. * @text_buf_size: The needed text buffer size. */ static inline void prb_rec_init_wr(struct printk_record *r, unsigned int text_buf_size) { r->info = NULL; r->text_buf = NULL; r->text_buf_size = text_buf_size; } bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb, struct printk_record *r); bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer *rb, struct printk_record *r, u32 caller_id, unsigned int max_size); void prb_commit(struct prb_reserved_entry *e); void prb_final_commit(struct prb_reserved_entry *e); void prb_init(struct printk_ringbuffer *rb, char *text_buf, unsigned int text_buf_size, struct prb_desc *descs, unsigned int descs_count_bits, struct printk_info *infos); unsigned int prb_record_text_space(struct prb_reserved_entry *e); /* Reader Interface */ /** * prb_rec_init_rd() - Initialize a buffer for reading records. * * @r: The record to initialize. * @info: A buffer to store record meta-data. * @text_buf: A buffer to store text data. * @text_buf_size: The size of @text_buf. * * Initialize all the fields that a reader is interested in. All arguments * (except @r) are optional. Only record data for arguments that are * non-NULL or non-zero will be read. */ static inline void prb_rec_init_rd(struct printk_record *r, struct printk_info *info, char *text_buf, unsigned int text_buf_size) { r->info = info; r->text_buf = text_buf; r->text_buf_size = text_buf_size; } /** * prb_for_each_record() - Iterate over the records of a ringbuffer. * * @from: The sequence number to begin with. * @rb: The ringbuffer to iterate over. * @s: A u64 to store the sequence number on each iteration. * @r: A printk_record to store the record on each iteration. * * This is a macro for conveniently iterating over a ringbuffer. * Note that @s may not be the sequence number of the record on each * iteration. For the sequence number, @r->info->seq should be checked. * * Context: Any context. */ #define prb_for_each_record(from, rb, s, r) \ for ((s) = from; prb_read_valid(rb, s, r); (s) = (r)->info->seq + 1) /** * prb_for_each_info() - Iterate over the meta data of a ringbuffer. * * @from: The sequence number to begin with. * @rb: The ringbuffer to iterate over. * @s: A u64 to store the sequence number on each iteration. * @i: A printk_info to store the record meta data on each iteration. * @lc: An unsigned int to store the text line count of each record. * * This is a macro for conveniently iterating over a ringbuffer. * Note that @s may not be the sequence number of the record on each * iteration. For the sequence number, @r->info->seq should be checked. * * Context: Any context. */ #define prb_for_each_info(from, rb, s, i, lc) \ for ((s) = from; prb_read_valid_info(rb, s, i, lc); (s) = (i)->seq + 1) bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq, struct printk_record *r); bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq, struct printk_info *info, unsigned int *line_count); u64 prb_first_seq(struct printk_ringbuffer *rb); u64 prb_first_valid_seq(struct printk_ringbuffer *rb); u64 prb_next_seq(struct printk_ringbuffer *rb); u64 prb_next_reserve_seq(struct printk_ringbuffer *rb); #ifdef CONFIG_64BIT #define __u64seq_to_ulseq(u64seq) (u64seq) #define __ulseq_to_u64seq(rb, ulseq) (ulseq) #define ULSEQ_MAX(rb) (-1) #else /* CONFIG_64BIT */ #define __u64seq_to_ulseq(u64seq) ((u32)u64seq) #define ULSEQ_MAX(rb) __u64seq_to_ulseq(prb_first_seq(rb) + 0x80000000UL) static inline u64 __ulseq_to_u64seq(struct printk_ringbuffer *rb, u32 ulseq) { u64 rb_first_seq = prb_first_seq(rb); u64 seq; /* * The provided sequence is only the lower 32 bits of the ringbuffer * sequence. It needs to be expanded to 64bit. Get the first sequence * number from the ringbuffer and fold it. * * Having a 32bit representation in the console is sufficient. * If a console ever gets more than 2^31 records behind * the ringbuffer then this is the least of the problems. * * Also the access to the ring buffer is always safe. */ seq = rb_first_seq - (s32)((u32)rb_first_seq - ulseq); return seq; } #endif /* CONFIG_64BIT */ #endif /* _KERNEL_PRINTK_RINGBUFFER_H */
