NAME¶

pmemlog_tell(), pmemlog_rewind(), pmemlog_walk() - checks current write point for the log or walks through the log

SYNOPSIS¶

#include <libpmemlog.h>
long long pmemlog_tell(PMEMlogpool *plp);
void pmemlog_rewind(PMEMlogpool *plp);
void pmemlog_walk(PMEMlogpool *plp, size_t chunksize,
    int (*process_chunk)(const void *buf, size_t len, void *arg),
    void *arg);

DESCRIPTION¶

The pmemlog_tell() function returns the current write point for the log, expressed as a byte offset into the usable log space in the memory pool. This offset starts off as zero on a newly-created log, and is incremented by each successful append operation. This function can be used to determine how much data is currently in the log.

The pmemlog_rewind() function resets the current write point for the log to zero. After this call, the next append adds to the beginning of the log.

The pmemlog_walk() function walks through the log plp, from beginning to end, calling the callback function process_chunk for each chunksize block of data found. The argument arg is also passed to the callback to help avoid the need for global state. The chunksize argument is useful for logs with fixed-length records and may be specified as 0 to cause a single call to the callback with the entire log contents passed as the buf argument. The len argument tells the process_chunk function how much data buf is holding. The callback function should return 1 if pmemlog_walk() should continue walking through the log, or 0 to terminate the walk. The callback function is called while holding libpmemlog(7) internal locks that make calls atomic, so the callback function must not try to append to the log itself or deadlock will occur.

RETURN VALUE¶

On success, pmemlog_tell() returns the current write point for the log. On error, it returns -1 and sets errno appropriately.

The pmemlog_rewind() and pmemlog_walk() functions return no value.

SEE ALSO¶

libpmemlog(7) and <https://pmem.io>