[PATCH] relay: migrate from relayfs to a generic relay API

Original patch from Paul Mundt, sysfs parts removed by me since they
were broken.

Signed-off-by: Jens Axboe <axboe@suse.de>

1 files changed, 281 insertions, 0 deletions

diff --git a/include/linux/relay.h b/include/linux/relay.h
new file mode 100644
index 000000000000..4bcc1531d6a9
--- /dev/null
+++ b/include/linux/relay.h
@@ -0,0 +1,281 @@
+/*
+ * linux/include/linux/relay.h
+ *
+ * Copyright (C) 2002, 2003 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
+ * Copyright (C) 1999, 2000, 2001, 2002 - Karim Yaghmour (karim@opersys.com)
+ *
+ * CONFIG_RELAY definitions and declarations
+ */
+
+#ifndef _LINUX_RELAY_H
+#define _LINUX_RELAY_H
+
+#include <linux/config.h>
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <linux/wait.h>
+#include <linux/list.h>
+#include <linux/fs.h>
+#include <linux/poll.h>
+#include <linux/kref.h>
+
+/* Needs a _much_ better name... */
+#define FIX_SIZE(x) ((((x) - 1) & PAGE_MASK) + PAGE_SIZE)
+
+/*
+ * Tracks changes to rchan/rchan_buf structs
+ */
+#define RELAYFS_CHANNEL_VERSION         6
+
+/*
+ * Per-cpu relay channel buffer
+ */
+struct rchan_buf
+{
+        void *start;                    /* start of channel buffer */
+        void *data;                     /* start of current sub-buffer */
+        size_t offset;                  /* current offset into sub-buffer */
+        size_t subbufs_produced;        /* count of sub-buffers produced */
+        size_t subbufs_consumed;        /* count of sub-buffers consumed */
+        struct rchan *chan;             /* associated channel */
+        wait_queue_head_t read_wait;    /* reader wait queue */
+        struct work_struct wake_readers; /* reader wake-up work struct */
+        struct dentry *dentry;          /* channel file dentry */
+        struct kref kref;               /* channel buffer refcount */
+        struct page **page_array;       /* array of current buffer pages */
+        unsigned int page_count;        /* number of current buffer pages */
+        unsigned int finalized;         /* buffer has been finalized */
+        size_t *padding;                /* padding counts per sub-buffer */
+        size_t prev_padding;            /* temporary variable */
+        size_t bytes_consumed;          /* bytes consumed in cur read subbuf */
+        unsigned int cpu;               /* this buf's cpu */
+} ____cacheline_aligned;
+
+/*
+ * Relay channel data structure
+ */
+struct rchan
+{
+        u32 version;                    /* the version of this struct */
+        size_t subbuf_size;             /* sub-buffer size */
+        size_t n_subbufs;               /* number of sub-buffers per buffer */
+        size_t alloc_size;              /* total buffer size allocated */
+        struct rchan_callbacks *cb;     /* client callbacks */
+        struct kref kref;               /* channel refcount */
+        void *private_data;             /* for user-defined data */
+        size_t last_toobig;             /* tried to log event > subbuf size */
+        struct rchan_buf *buf[NR_CPUS]; /* per-cpu channel buffers */
+};
+
+/*
+ * Relay channel client callbacks
+ */
+struct rchan_callbacks
+{
+        /*
+         * subbuf_start - called on buffer-switch to a new sub-buffer
+         * @buf: the channel buffer containing the new sub-buffer
+         * @subbuf: the start of the new sub-buffer
+         * @prev_subbuf: the start of the previous sub-buffer
+         * @prev_padding: unused space at the end of previous sub-buffer
+         *
+         * The client should return 1 to continue logging, 0 to stop
+         * logging.
+         *
+         * NOTE: subbuf_start will also be invoked when the buffer is
+         *       created, so that the first sub-buffer can be initialized
+         *       if necessary.  In this case, prev_subbuf will be NULL.
+         *
+         * NOTE: the client can reserve bytes at the beginning of the new
+         *       sub-buffer by calling subbuf_start_reserve() in this callback.
+         */
+        int (*subbuf_start) (struct rchan_buf *buf,
+                             void *subbuf,
+                             void *prev_subbuf,
+                             size_t prev_padding);
+
+        /*
+         * buf_mapped - relay buffer mmap notification
+         * @buf: the channel buffer
+         * @filp: relay file pointer
+         *
+         * Called when a relay file is successfully mmapped
+         */
+        void (*buf_mapped)(struct rchan_buf *buf,
+                           struct file *filp);
+
+        /*
+         * buf_unmapped - relay buffer unmap notification
+         * @buf: the channel buffer
+         * @filp: relay file pointer
+         *
+         * Called when a relay file is successfully unmapped
+         */
+        void (*buf_unmapped)(struct rchan_buf *buf,
+                             struct file *filp);
+        /*
+         * create_buf_file - create file to represent a relay channel buffer
+         * @filename: the name of the file to create
+         * @parent: the parent of the file to create
+         * @mode: the mode of the file to create
+         * @buf: the channel buffer
+         * @is_global: outparam - set non-zero if the buffer should be global
+         *
+         * Called during relay_open(), once for each per-cpu buffer,
+         * to allow the client to create a file to be used to
+         * represent the corresponding channel buffer.  If the file is
+         * created outside of relay, the parent must also exist in
+         * that filesystem.
+         *
+         * The callback should return the dentry of the file created
+         * to represent the relay buffer.
+         *
+         * Setting the is_global outparam to a non-zero value will
+         * cause relay_open() to create a single global buffer rather
+         * than the default set of per-cpu buffers.
+         *
+         * See Documentation/filesystems/relayfs.txt for more info.
+         */
+        struct dentry *(*create_buf_file)(const char *filename,
+                                          struct dentry *parent,
+                                          int mode,
+                                          struct rchan_buf *buf,
+                                          int *is_global);
+
+        /*
+         * remove_buf_file - remove file representing a relay channel buffer
+         * @dentry: the dentry of the file to remove
+         *
+         * Called during relay_close(), once for each per-cpu buffer,
+         * to allow the client to remove a file used to represent a
+         * channel buffer.
+         *
+         * The callback should return 0 if successful, negative if not.
+         */
+        int (*remove_buf_file)(struct dentry *dentry);
+};
+
+/*
+ * CONFIG_RELAY kernel API, kernel/relay.c
+ */
+
+struct rchan *relay_open(const char *base_filename,
+                         struct dentry *parent,
+                         size_t subbuf_size,
+                         size_t n_subbufs,
+                         struct rchan_callbacks *cb);
+extern void relay_close(struct rchan *chan);
+extern void relay_flush(struct rchan *chan);
+extern void relay_subbufs_consumed(struct rchan *chan,
+                                   unsigned int cpu,
+                                   size_t consumed);
+extern void relay_reset(struct rchan *chan);
+extern int relay_buf_full(struct rchan_buf *buf);
+
+extern size_t relay_switch_subbuf(struct rchan_buf *buf,
+                                  size_t length);
+
+/**
+ *      relay_write - write data into the channel
+ *      @chan: relay channel
+ *      @data: data to be written
+ *      @length: number of bytes to write
+ *
+ *      Writes data into the current cpu's channel buffer.
+ *
+ *      Protects the buffer by disabling interrupts.  Use this
+ *      if you might be logging from interrupt context.  Try
+ *      __relay_write() if you know you won't be logging from
+ *      interrupt context.
+ */
+static inline void relay_write(struct rchan *chan,
+                               const void *data,
+                               size_t length)
+{
+        unsigned long flags;
+        struct rchan_buf *buf;
+
+        local_irq_save(flags);
+        buf = chan->buf[smp_processor_id()];
+        if (unlikely(buf->offset + length > chan->subbuf_size))
+                length = relay_switch_subbuf(buf, length);
+        memcpy(buf->data + buf->offset, data, length);
+        buf->offset += length;
+        local_irq_restore(flags);
+}
+
+/**
+ *      __relay_write - write data into the channel
+ *      @chan: relay channel
+ *      @data: data to be written
+ *      @length: number of bytes to write
+ *
+ *      Writes data into the current cpu's channel buffer.
+ *
+ *      Protects the buffer by disabling preemption.  Use
+ *      relay_write() if you might be logging from interrupt
+ *      context.
+ */
+static inline void __relay_write(struct rchan *chan,
+                                 const void *data,
+                                 size_t length)
+{
+        struct rchan_buf *buf;
+
+        buf = chan->buf[get_cpu()];
+        if (unlikely(buf->offset + length > buf->chan->subbuf_size))
+                length = relay_switch_subbuf(buf, length);
+        memcpy(buf->data + buf->offset, data, length);
+        buf->offset += length;
+        put_cpu();
+}
+
+/**
+ *      relay_reserve - reserve slot in channel buffer
+ *      @chan: relay channel
+ *      @length: number of bytes to reserve
+ *
+ *      Returns pointer to reserved slot, NULL if full.
+ *
+ *      Reserves a slot in the current cpu's channel buffer.
+ *      Does not protect the buffer at all - caller must provide
+ *      appropriate synchronization.
+ */
+static inline void *relay_reserve(struct rchan *chan, size_t length)
+{
+        void *reserved;
+        struct rchan_buf *buf = chan->buf[smp_processor_id()];
+
+        if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
+                length = relay_switch_subbuf(buf, length);
+                if (!length)
+                        return NULL;
+        }
+        reserved = buf->data + buf->offset;
+        buf->offset += length;
+
+        return reserved;
+}
+
+/**
+ *      subbuf_start_reserve - reserve bytes at the start of a sub-buffer
+ *      @buf: relay channel buffer
+ *      @length: number of bytes to reserve
+ *
+ *      Helper function used to reserve bytes at the beginning of
+ *      a sub-buffer in the subbuf_start() callback.
+ */
+static inline void subbuf_start_reserve(struct rchan_buf *buf,
+                                        size_t length)
+{
+        BUG_ON(length >= buf->chan->subbuf_size - 1);
+        buf->offset = length;
+}
+
+/*
+ * exported relay file operations, kernel/relay.c
+ */
+extern struct file_operations relay_file_operations;
+
+#endif /* _LINUX_RELAY_H */
+