[PATCH 47/60] xfs: separate out log format definitions

Dave Chinner
2013-06-19T04:52:54Z

From: Dave Chinner <dchinner@redhat.com>

The on-disk format definitions for the log are spread randoms
through a couple of header files. Consolidate it all in a single
file that can be shared easily with userspace. This means that
xfs_log.h and xfs_log_priv.h no longer need to be shared with
userspace.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/xfs_log.h | 89 ++++++-----------------
fs/xfs/xfs_log_format.h | 178 ++++++++++++++++++++++++++++++++++++++++++++++
fs/xfs/xfs_log_priv.h | 146 ++-----------------------------------
fs/xfs/xfs_log_recover.c | 2 +
4 files changed, 207 insertions(+), 208 deletions(-)
create mode 100644 fs/xfs/xfs_log_format.h

diff --git a/fs/xfs/xfs_log.h b/fs/xfs/xfs_log.h
index fb630e4..e63d9e1 100644
--- a/fs/xfs/xfs_log.h
+++ b/fs/xfs/xfs_log.h
@@ -18,14 +18,29 @@
#ifndef __XFS_LOG_H__
#define __XFS_LOG_H__

-/* get lsn fields */
-#define CYCLE_LSN(lsn) ((uint)((lsn)>>32))
-#define BLOCK_LSN(lsn) ((uint)(lsn))
+#include "xfs_log_format.h"

-/* this is used in a spot where we might otherwise double-endian-flip */
-#define CYCLE_LSN_DISK(lsn) (((__be32 *)&(lsn))[0])
+struct xfs_log_vec {
+ struct xfs_log_vec *lv_next; /* next lv in build list */
+ int lv_niovecs; /* number of iovecs in lv */
+ struct xfs_log_iovec *lv_iovecp; /* iovec array */
+ struct xfs_log_item *lv_item; /* owner */
+ char *lv_buf; /* formatted buffer */
+ int lv_buf_len; /* size of formatted buffer */
+};
+
+#define XFS_LOG_VEC_ORDERED (-1)
+
+/*
+ * Structure used to pass callback function and the function's argument
+ * to the log manager.
+ */
+typedef struct xfs_log_callback {
+ struct xfs_log_callback *cb_next;
+ void (*cb_func)(void *, int);
+ void *cb_arg;
+} xfs_log_callback_t;

-#ifdef __KERNEL__
/*
* By comparing each component, we don't have to worry about extra
* endian issues in treating two 32 bit numbers as one 64 bit number
@@ -59,67 +74,6 @@ static inline xfs_lsn_t _lsn_cmp(xfs_lsn_t lsn1, xfs_lsn_t lsn2)
*/
#define XFS_LOG_SYNC 0x1

-#endif /* __KERNEL__ */
-
-
-/* Log Clients */
-#define XFS_TRANSACTION 0x69
-#define XFS_VOLUME 0x2
-#define XFS_LOG 0xaa
-
-
-/* Region types for iovec's i_type */
-#define XLOG_REG_TYPE_BFORMAT 1
-#define XLOG_REG_TYPE_BCHUNK 2
-#define XLOG_REG_TYPE_EFI_FORMAT 3
-#define XLOG_REG_TYPE_EFD_FORMAT 4
-#define XLOG_REG_TYPE_IFORMAT 5
-#define XLOG_REG_TYPE_ICORE 6
-#define XLOG_REG_TYPE_IEXT 7
-#define XLOG_REG_TYPE_IBROOT 8
-#define XLOG_REG_TYPE_ILOCAL 9
-#define XLOG_REG_TYPE_IATTR_EXT 10
-#define XLOG_REG_TYPE_IATTR_BROOT 11
-#define XLOG_REG_TYPE_IATTR_LOCAL 12
-#define XLOG_REG_TYPE_QFORMAT 13
-#define XLOG_REG_TYPE_DQUOT 14
-#define XLOG_REG_TYPE_QUOTAOFF 15
-#define XLOG_REG_TYPE_LRHEADER 16
-#define XLOG_REG_TYPE_UNMOUNT 17
-#define XLOG_REG_TYPE_COMMIT 18
-#define XLOG_REG_TYPE_TRANSHDR 19
-#define XLOG_REG_TYPE_ICREATE 20
-#define XLOG_REG_TYPE_MAX 20
-
-typedef struct xfs_log_iovec {
- void *i_addr; /* beginning address of region */
- int i_len; /* length in bytes of region */
- uint i_type; /* type of region */
-} xfs_log_iovec_t;
-
-struct xfs_log_vec {
- struct xfs_log_vec *lv_next; /* next lv in build list */
- int lv_niovecs; /* number of iovecs in lv */
- struct xfs_log_iovec *lv_iovecp; /* iovec array */
- struct xfs_log_item *lv_item; /* owner */
- char *lv_buf; /* formatted buffer */
- int lv_buf_len; /* size of formatted buffer */
-};
-
-#define XFS_LOG_VEC_ORDERED (-1)
-
-/*
- * Structure used to pass callback function and the function's argument
- * to the log manager.
- */
-typedef struct xfs_log_callback {
- struct xfs_log_callback *cb_next;
- void (*cb_func)(void *, int);
- void *cb_arg;
-} xfs_log_callback_t;
-
-
-#ifdef __KERNEL__
/* Log manager interfaces */
struct xfs_mount;
struct xlog_in_core;
@@ -188,5 +142,4 @@ void xfs_log_work_queue(struct xfs_mount *mp);
void xfs_log_worker(struct work_struct *work);
void xfs_log_quiesce(struct xfs_mount *mp);

-#endif
#endif /* __XFS_LOG_H__ */
diff --git a/fs/xfs/xfs_log_format.h b/fs/xfs/xfs_log_format.h
new file mode 100644
index 0000000..9f9aeb6
--- /dev/null
+++ b/fs/xfs/xfs_log_format.h
@@ -0,0 +1,178 @@
+/*
+ * Copyright (c) 2000-2003,2005 Silicon Graphics, Inc.
+ * All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+#ifndef __XFS_LOG_FORMAT_H__
+#define __XFS_LOG_FORMAT_H__
+
+typedef __uint32_t xlog_tid_t;
+
+#define XLOG_MIN_ICLOGS 2
+#define XLOG_MAX_ICLOGS 8
+#define XLOG_HEADER_MAGIC_NUM 0xFEEDbabe /* Invalid cycle number */
+#define XLOG_VERSION_1 1
+#define XLOG_VERSION_2 2 /* Large IClogs, Log sunit */
+#define XLOG_VERSION_OKBITS (XLOG_VERSION_1 | XLOG_VERSION_2)
+#define XLOG_MIN_RECORD_BSIZE (16*1024) /* eventually 32k */
+#define XLOG_BIG_RECORD_BSIZE (32*1024) /* 32k buffers */
+#define XLOG_MAX_RECORD_BSIZE (256*1024)
+#define XLOG_HEADER_CYCLE_SIZE (32*1024) /* cycle data in header */
+#define XLOG_MIN_RECORD_BSHIFT 14 /* 16384 == 1 << 14 */
+#define XLOG_BIG_RECORD_BSHIFT 15 /* 32k == 1 << 15 */
+#define XLOG_MAX_RECORD_BSHIFT 18 /* 256k == 1 << 18 */
+#define XLOG_BTOLSUNIT(log, b) (((b)+(log)->l_mp->m_sb.sb_logsunit-1) / \
+ (log)->l_mp->m_sb.sb_logsunit)
+#define XLOG_LSUNITTOB(log, su) ((su) * (log)->l_mp->m_sb.sb_logsunit)
+
+#define XLOG_HEADER_SIZE 512
+
+#define XLOG_REC_SHIFT(log) \
+ BTOBB(1 << (xfs_sb_version_haslogv2(&log->l_mp->m_sb) ? \
+ XLOG_MAX_RECORD_BSHIFT : XLOG_BIG_RECORD_BSHIFT))
+#define XLOG_TOTAL_REC_SHIFT(log) \
+ BTOBB(XLOG_MAX_ICLOGS << (xfs_sb_version_haslogv2(&log->l_mp->m_sb) ? \
+ XLOG_MAX_RECORD_BSHIFT : XLOG_BIG_RECORD_BSHIFT))
+
+/* get lsn fields */
+#define CYCLE_LSN(lsn) ((uint)((lsn)>>32))
+#define BLOCK_LSN(lsn) ((uint)(lsn))
+
+/* this is used in a spot where we might otherwise double-endian-flip */
+#define CYCLE_LSN_DISK(lsn) (((__be32 *)&(lsn))[0])
+
+static inline xfs_lsn_t xlog_assign_lsn(uint cycle, uint block)
+{
+ return ((xfs_lsn_t)cycle << 32) | block;
+}
+
+static inline uint xlog_get_cycle(char *ptr)
+{
+ if (be32_to_cpu(*(__be32 *)ptr) == XLOG_HEADER_MAGIC_NUM)
+ return be32_to_cpu(*((__be32 *)ptr + 1));
+ else
+ return be32_to_cpu(*(__be32 *)ptr);
+}
+
+/* Log Clients */
+#define XFS_TRANSACTION 0x69
+#define XFS_VOLUME 0x2
+#define XFS_LOG 0xaa
+
+#define XLOG_UNMOUNT_TYPE 0x556e /* Un for Unmount */
+
+/* Region types for iovec's i_type */
+#define XLOG_REG_TYPE_BFORMAT 1
+#define XLOG_REG_TYPE_BCHUNK 2
+#define XLOG_REG_TYPE_EFI_FORMAT 3
+#define XLOG_REG_TYPE_EFD_FORMAT 4
+#define XLOG_REG_TYPE_IFORMAT 5
+#define XLOG_REG_TYPE_ICORE 6
+#define XLOG_REG_TYPE_IEXT 7
+#define XLOG_REG_TYPE_IBROOT 8
+#define XLOG_REG_TYPE_ILOCAL 9
+#define XLOG_REG_TYPE_IATTR_EXT 10
+#define XLOG_REG_TYPE_IATTR_BROOT 11
+#define XLOG_REG_TYPE_IATTR_LOCAL 12
+#define XLOG_REG_TYPE_QFORMAT 13
+#define XLOG_REG_TYPE_DQUOT 14
+#define XLOG_REG_TYPE_QUOTAOFF 15
+#define XLOG_REG_TYPE_LRHEADER 16
+#define XLOG_REG_TYPE_UNMOUNT 17
+#define XLOG_REG_TYPE_COMMIT 18
+#define XLOG_REG_TYPE_TRANSHDR 19
+#define XLOG_REG_TYPE_ICREATE 20
+#define XLOG_REG_TYPE_MAX 20
+
+/*
+ * Flags to log operation header
+ *
+ * The first write of a new transaction will be preceded with a start
+ * record, XLOG_START_TRANS. Once a transaction is committed, a commit
+ * record is written, XLOG_COMMIT_TRANS. If a single region can not fit into
+ * the remainder of the current active in-core log, it is split up into
+ * multiple regions. Each partial region will be marked with a
+ * XLOG_CONTINUE_TRANS until the last one, which gets marked with XLOG_END_TRANS.
+ *
+ */
+#define XLOG_START_TRANS 0x01 /* Start a new transaction */
+#define XLOG_COMMIT_TRANS 0x02 /* Commit this transaction */
+#define XLOG_CONTINUE_TRANS 0x04 /* Cont this trans into new region */
+#define XLOG_WAS_CONT_TRANS 0x08 /* Cont this trans into new region */
+#define XLOG_END_TRANS 0x10 /* End a continued transaction */
+#define XLOG_UNMOUNT_TRANS 0x20 /* Unmount a filesystem transaction */
+
+
+typedef struct xlog_op_header {
+ __be32 oh_tid; /* transaction id of operation : 4 b */
+ __be32 oh_len; /* bytes in data region : 4 b */
+ __u8 oh_clientid; /* who sent me this : 1 b */
+ __u8 oh_flags; /* : 1 b */
+ __u16 oh_res2; /* 32 bit align : 2 b */
+} xlog_op_header_t;
+
+
+/* valid values for h_fmt */
+#define XLOG_FMT_UNKNOWN 0
+#define XLOG_FMT_LINUX_LE 1
+#define XLOG_FMT_LINUX_BE 2
+#define XLOG_FMT_IRIX_BE 3
+
+/* our fmt */
+#ifdef XFS_NATIVE_HOST
+#define XLOG_FMT XLOG_FMT_LINUX_BE
+#else
+#define XLOG_FMT XLOG_FMT_LINUX_LE
+#endif
+
+typedef struct xlog_rec_header {
+ __be32 h_magicno; /* log record (LR) identifier : 4 */
+ __be32 h_cycle; /* write cycle of log : 4 */
+ __be32 h_version; /* LR version : 4 */
+ __be32 h_len; /* len in bytes; should be 64-bit aligned: 4 */
+ __be64 h_lsn; /* lsn of this LR : 8 */
+ __be64 h_tail_lsn; /* lsn of 1st LR w/ buffers not committed: 8 */
+ __le32 h_crc; /* crc of log record : 4 */
+ __be32 h_prev_block; /* block number to previous LR : 4 */
+ __be32 h_num_logops; /* number of log operations in this LR : 4 */
+ __be32 h_cycle_data[XLOG_HEADER_CYCLE_SIZE / BBSIZE];
+ /* new fields */
+ __be32 h_fmt; /* format of log record : 4 */
+ uuid_t h_fs_uuid; /* uuid of FS : 16 */
+ __be32 h_size; /* iclog size : 4 */
+} xlog_rec_header_t;
+
+typedef struct xlog_rec_ext_header {
+ __be32 xh_cycle; /* write cycle of log : 4 */
+ __be32 xh_cycle_data[XLOG_HEADER_CYCLE_SIZE / BBSIZE]; /* : 256 */
+} xlog_rec_ext_header_t;
+
+/*
+ * Quite misnamed, because this union lays out the actual on-disk log buffer.
+ */
+typedef union xlog_in_core2 {
+ xlog_rec_header_t hic_header;
+ xlog_rec_ext_header_t hic_xheader;
+ char hic_sector[XLOG_HEADER_SIZE];
+} xlog_in_core_2_t;
+
+/* not an on-disk structure, but needed by log recovery in userspace */
+typedef struct xfs_log_iovec {
+ void *i_addr; /* beginning address of region */
+ int i_len; /* length in bytes of region */
+ uint i_type; /* type of region */
+} xfs_log_iovec_t;
+
+#endif /* __XFS_LOG_FORMAT_H__ */
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index b9ea262..edd0964 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -24,51 +24,13 @@ struct xlog_ticket;
struct xfs_mount;

/*
- * Macros, structures, prototypes for internal log manager use.
+ * Flags for log structure
*/
-
-#define XLOG_MIN_ICLOGS 2
-#define XLOG_MAX_ICLOGS 8
-#define XLOG_HEADER_MAGIC_NUM 0xFEEDbabe /* Invalid cycle number */
-#define XLOG_VERSION_1 1
-#define XLOG_VERSION_2 2 /* Large IClogs, Log sunit */
-#define XLOG_VERSION_OKBITS (XLOG_VERSION_1 | XLOG_VERSION_2)
-#define XLOG_MIN_RECORD_BSIZE (16*1024) /* eventually 32k */
-#define XLOG_BIG_RECORD_BSIZE (32*1024) /* 32k buffers */
-#define XLOG_MAX_RECORD_BSIZE (256*1024)
-#define XLOG_HEADER_CYCLE_SIZE (32*1024) /* cycle data in header */
-#define XLOG_MIN_RECORD_BSHIFT 14 /* 16384 == 1 << 14 */
-#define XLOG_BIG_RECORD_BSHIFT 15 /* 32k == 1 << 15 */
-#define XLOG_MAX_RECORD_BSHIFT 18 /* 256k == 1 << 18 */
-#define XLOG_BTOLSUNIT(log, b) (((b)+(log)->l_mp->m_sb.sb_logsunit-1) / \
- (log)->l_mp->m_sb.sb_logsunit)
-#define XLOG_LSUNITTOB(log, su) ((su) * (log)->l_mp->m_sb.sb_logsunit)
-
-#define XLOG_HEADER_SIZE 512
-
-#define XLOG_REC_SHIFT(log) \
- BTOBB(1 << (xfs_sb_version_haslogv2(&log->l_mp->m_sb) ? \
- XLOG_MAX_RECORD_BSHIFT : XLOG_BIG_RECORD_BSHIFT))
-#define XLOG_TOTAL_REC_SHIFT(log) \
- BTOBB(XLOG_MAX_ICLOGS << (xfs_sb_version_haslogv2(&log->l_mp->m_sb) ? \
- XLOG_MAX_RECORD_BSHIFT : XLOG_BIG_RECORD_BSHIFT))
-
-static inline xfs_lsn_t xlog_assign_lsn(uint cycle, uint block)
-{
- return ((xfs_lsn_t)cycle << 32) | block;
-}
-
-static inline uint xlog_get_cycle(char *ptr)
-{
- if (be32_to_cpu(*(__be32 *)ptr) == XLOG_HEADER_MAGIC_NUM)
- return be32_to_cpu(*((__be32 *)ptr + 1));
- else
- return be32_to_cpu(*(__be32 *)ptr);
-}
-
-#define BLK_AVG(blk1, blk2) ((blk1+blk2) >> 1)
-
-#ifdef __KERNEL__
+#define XLOG_ACTIVE_RECOVERY 0x2 /* in the middle of recovery */
+#define XLOG_RECOVERY_NEEDED 0x4 /* log was recovered */
+#define XLOG_IO_ERROR 0x8 /* log hit an I/O error, and being
+ shutdown */
+#define XLOG_TAIL_WARN 0x10 /* log tail verify warning issued */

/*
* get client id from packed copy.
@@ -101,28 +63,8 @@ static inline uint xlog_get_client_id(__be32 i)
#define XLOG_STATE_IOERROR 0x0080 /* IO error happened in sync'ing log */
#define XLOG_STATE_ALL 0x7FFF /* All possible valid flags */
#define XLOG_STATE_NOTUSED 0x8000 /* This IC log not being used */
-#endif /* __KERNEL__ */

/*
- * Flags to log operation header
- *
- * The first write of a new transaction will be preceded with a start
- * record, XLOG_START_TRANS. Once a transaction is committed, a commit
- * record is written, XLOG_COMMIT_TRANS. If a single region can not fit into
- * the remainder of the current active in-core log, it is split up into
- * multiple regions. Each partial region will be marked with a
- * XLOG_CONTINUE_TRANS until the last one, which gets marked with XLOG_END_TRANS.
- *
- */
-#define XLOG_START_TRANS 0x01 /* Start a new transaction */
-#define XLOG_COMMIT_TRANS 0x02 /* Commit this transaction */
-#define XLOG_CONTINUE_TRANS 0x04 /* Cont this trans into new region */
-#define XLOG_WAS_CONT_TRANS 0x08 /* Cont this trans into new region */
-#define XLOG_END_TRANS 0x10 /* End a continued transaction */
-#define XLOG_UNMOUNT_TRANS 0x20 /* Unmount a filesystem transaction */
-
-#ifdef __KERNEL__
-/*
* Flags to log ticket
*/
#define XLOG_TIC_INITED 0x1 /* has been initialized */
@@ -132,22 +74,6 @@ static inline uint xlog_get_client_id(__be32 i)
{ XLOG_TIC_INITED, "XLOG_TIC_INITED" }, \
{ XLOG_TIC_PERM_RESERV, "XLOG_TIC_PERM_RESERV" }

-#endif /* __KERNEL__ */
-
-#define XLOG_UNMOUNT_TYPE 0x556e /* Un for Unmount */
-
-/*
- * Flags for log structure
- */
-#define XLOG_ACTIVE_RECOVERY 0x2 /* in the middle of recovery */
-#define XLOG_RECOVERY_NEEDED 0x4 /* log was recovered */
-#define XLOG_IO_ERROR 0x8 /* log hit an I/O error, and being
- shutdown */
-#define XLOG_TAIL_WARN 0x10 /* log tail verify warning issued */
-
-typedef __uint32_t xlog_tid_t;
-
-#ifdef __KERNEL__
/*
* Below are states for covering allocation transactions.
* By covering, we mean changing the h_tail_lsn in the last on-disk
@@ -223,7 +149,6 @@ typedef __uint32_t xlog_tid_t;

#define XLOG_COVER_OPS 5

-
/* Ticket reservation region accounting */
#define XLOG_TIC_LEN_MAX 15

@@ -258,64 +183,6 @@ typedef struct xlog_ticket {
xlog_res_t t_res_arr[XLOG_TIC_LEN_MAX]; /* array of res : 8 * 15 */
} xlog_ticket_t;

-#endif
-
-
-typedef struct xlog_op_header {
- __be32 oh_tid; /* transaction id of operation : 4 b */
- __be32 oh_len; /* bytes in data region : 4 b */
- __u8 oh_clientid; /* who sent me this : 1 b */
- __u8 oh_flags; /* : 1 b */
- __u16 oh_res2; /* 32 bit align : 2 b */
-} xlog_op_header_t;
-
-
-/* valid values for h_fmt */
-#define XLOG_FMT_UNKNOWN 0
-#define XLOG_FMT_LINUX_LE 1
-#define XLOG_FMT_LINUX_BE 2
-#define XLOG_FMT_IRIX_BE 3
-
-/* our fmt */
-#ifdef XFS_NATIVE_HOST
-#define XLOG_FMT XLOG_FMT_LINUX_BE
-#else
-#define XLOG_FMT XLOG_FMT_LINUX_LE
-#endif
-
-typedef struct xlog_rec_header {
- __be32 h_magicno; /* log record (LR) identifier : 4 */
- __be32 h_cycle; /* write cycle of log : 4 */
- __be32 h_version; /* LR version : 4 */
- __be32 h_len; /* len in bytes; should be 64-bit aligned: 4 */
- __be64 h_lsn; /* lsn of this LR : 8 */
- __be64 h_tail_lsn; /* lsn of 1st LR w/ buffers not committed: 8 */
- __le32 h_crc; /* crc of log record : 4 */
- __be32 h_prev_block; /* block number to previous LR : 4 */
- __be32 h_num_logops; /* number of log operations in this LR : 4 */
- __be32 h_cycle_data[XLOG_HEADER_CYCLE_SIZE / BBSIZE];
- /* new fields */
- __be32 h_fmt; /* format of log record : 4 */
- uuid_t h_fs_uuid; /* uuid of FS : 16 */
- __be32 h_size; /* iclog size : 4 */
-} xlog_rec_header_t;
-
-typedef struct xlog_rec_ext_header {
- __be32 xh_cycle; /* write cycle of log : 4 */
- __be32 xh_cycle_data[XLOG_HEADER_CYCLE_SIZE / BBSIZE]; /* : 256 */
-} xlog_rec_ext_header_t;
-
-#ifdef __KERNEL__
-
-/*
- * Quite misnamed, because this union lays out the actual on-disk log buffer.
- */
-typedef union xlog_in_core2 {
- xlog_rec_header_t hic_header;
- xlog_rec_ext_header_t hic_xheader;
- char hic_sector[XLOG_HEADER_SIZE];
-} xlog_in_core_2_t;
-
/*
* - A log record header is 512 bytes. There is plenty of room to grow the
* xlog_rec_header_t into the reserved space.
@@ -686,6 +553,5 @@ static inline void xlog_wait(wait_queue_head_t *wq, spinlock_t *lock)
schedule();
remove_wait_queue(wq, &wait);
}
-#endif /* __KERNEL__ */

#endif /* __XFS_LOG_PRIV_H__ */
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 8a810fe..f840cb9 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -54,6 +54,8 @@
#include "xfs_attr_leaf.h"
#include "xfs_attr_remote.h"

+#define BLK_AVG(blk1, blk2) ((blk1+blk2) >> 1)
+
STATIC int
xlog_find_zeroed(
struct xlog *,