NAME¶

SYNOPSIS¶

#include <librpmem.h>
int rpmem_persist(RPMEMpool *rpp, size_t offset,
    size_t length, unsigned lane, unsigned flags);
int rpmem_deep_persist(RPMEMpool *rpp, size_t offset,
    size_t length, unsigned lane);
int rpmem_flush(RPMEMpool *rpp, size_t offset,
    size_t length, unsigned lane, unsigned flags);
int rpmem_drain(RPMEMpool *rpp, unsigned lane, unsigned flags);
int rpmem_read(RPMEMpool *rpp, void *buff, size_t offset,
    size_t length, unsigned lane);

    

DESCRIPTION¶

The rpmem_deep_persist() function works in the same way as rpmem_persist(3) function, but additionally it flushes the data to the lowest possible persistency domain available from software. Please see pmem_deep_persist(3) for details.

The rpmem_flush() and rpmem_drain() functions are two halves of the single rpmem_persist(). The rpmem_persist() copies data and makes it persistent in the one shot, where rpmem_flush() and rpmem_drain() split this operation into two stages. The rpmem_flush() copies data of given length at a given offset from the associated local memory pool to the remote node. The rpmem_drain() makes sure the data copied in all preceding rpmem_flush() calls is persistent on the remote node before the function returns. Data copied using rpmem_flush() can not be considered persistent on the remote node before return from following rpmem_drain(). Single rpmem_drain() confirms persistence on the remote node of data copied by all rpmem_flush() functions called before it and using the same lane. The last rpmem_flush() + rpmem_drain() can be replaced with rpmem_persist() at no cost.

The flags argument for rpmem_flush() can be 0 or RPMEM_FLUSH_RELAXED which means the flush operation will be done without any guarantees regarding atomicity of memory transfer. The flags argument for rpmem_drain() must be 0.

The rpmem_flush() function performance is affected by RPMEM_WORK_QUEUE_SIZE environment variable (see librpmem(7) for more details).

The rpmem_read() function reads length bytes of data from a remote pool at offset and copies it to the buffer buff. The operation is performed on the specified lane. The lane must be less than the value returned by rpmem_open(3) or rpmem_create(3) through the nlanes argument (so it can take a value from 0 to nlanes - 1). The rpp must point to a remote pool opened or created previously by rpmem_open(3) or rpmem_create(3).

RETURN VALUE¶

The rpmem_flush() function returns 0 if duplication of the memory area to the remote node was initialized successfully. Otherwise, it returns a non-zero value and sets errno appropriately.

The rpmem_drain() function returns 0 if the memory areas duplicated by all rpmem_flush() calls preceding the rpmem_drain() are made persistent on the remote node. Otherwise, it returns a non-zero value and sets errno appropriately.

The rpmem_read() function returns 0 if the data was read entirely. Otherwise it returns a non-zero value and sets errno appropriately.

CAVEATS¶

SEE ALSO¶