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G_DATA(9) FreeBSD Kernel Developer's Manual G_DATA(9)

g_read_data, g_write_data
read/write data from/to GEOM consumer

#include <geom/geom.h>
void *
g_read_data(struct g_consumer *cp, off_t offset, off_t length, int *error);
g_write_data(struct g_consumer *cp, off_t offset, void *ptr, off_t length);

The g_read_data() function reads length bytes of data from the provider attached to consumer cp, starting at offset offset. The buffer returned from g_read_data() is allocated with g_malloc(), so it should be freed by the caller with g_free() after use. If the operation fails, an error value will be stored in the error argument if it is not NULL.
The g_write_data() function writes length bytes of data from the buffer pointed to by ptr to the provider attached to consumer cp, starting at offset offset.

The length argument should be a multiple of the provider's sectorsize and less than or equal to DFLTPHYS (DFLTPHYS is defined in <sys/param.h>).
The topology lock must not be held.

The g_read_data() function returns a pointer to a data buffer or NULL if an error occurred. In that case an error value is stored in the error argument unless it is NULL.
The g_write_data() function returns 0 if successful; otherwise an error code is returned.

Possible errors:
An I/O error occurred while reading from or writing to the consumer.

geom(4), DECLARE_GEOM_CLASS(9), g_access(9), g_attach(9), g_bio(9), g_consumer(9), g_event(9), g_geom(9), g_provider(9), g_provider_by_name(9), g_wither_geom(9)

This manual page was written by Pawel Jakub Dawidek <>.
January 16, 2004 FreeBSD 12.0-RELEASE

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