fd935ce4c9
The three-way hand-off has a problem: there's no way to arrange for the state of the migration to be unambiguous in case of failure. If the final "disconnect" message is lost (as in, the destination never receives it whether it is sent by the sender or not), the destination has no option but to quit with an error status and let a human sort it out. However, at that point we can either arrange to have a .INCOMPLETE file still on disc or not - and it doesn't matter which we choose, we can still end up with dataloss by picking a specific calamity to have befallen the sender. Given this, it makes sense to fall back to a simpler protocol: just send all the data, then send a "disconnect" message. This has the same downside that we need a human to sort out specific failure cases, but combined with --unlink before sending "disconnect" (see next patch) it will always be possible for a human to disambiguate, whether the destination quit with an error status or not.
77 lines
1.8 KiB
C
77 lines
1.8 KiB
C
#ifndef __NBDTYPES_H
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#define __NBDTYPES_H
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/* http://linux.derkeiler.com/Mailing-Lists/Kernel/2003-09/2332.html */
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#define INIT_PASSWD "NBDMAGIC"
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#define INIT_MAGIC 0x0000420281861253
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#define REQUEST_MAGIC 0x25609513
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#define REPLY_MAGIC 0x67446698
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#define REQUEST_READ 0
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#define REQUEST_WRITE 1
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#define REQUEST_DISCONNECT 2
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#include <linux/types.h>
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#include <inttypes.h>
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/* The _raw types are the types as they appear on the wire. Non-_raw
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* types are in host-format.
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* Conversion functions are _r2h_ for converting raw to host, and _h2r_
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* for converting host to raw.
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*/
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struct nbd_init_raw {
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char passwd[8];
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__be64 magic;
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__be64 size;
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char reserved[128];
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};
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struct nbd_request_raw {
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__be32 magic;
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__be32 type; /* == READ || == WRITE */
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char handle[8];
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__be64 from;
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__be32 len;
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} __attribute__((packed));
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struct nbd_reply_raw {
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__be32 magic;
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__be32 error; /* 0 = ok, else error */
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char handle[8]; /* handle you got from request */
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};
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struct nbd_init {
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char passwd[8];
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uint64_t magic;
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uint64_t size;
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char reserved[128];
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};
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struct nbd_request {
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uint32_t magic;
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uint32_t type; /* == READ || == WRITE */
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char handle[8];
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uint64_t from;
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uint32_t len;
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} __attribute__((packed));
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struct nbd_reply {
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uint32_t magic;
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uint32_t error; /* 0 = ok, else error */
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char handle[8]; /* handle you got from request */
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};
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void nbd_r2h_init( struct nbd_init_raw * from, struct nbd_init * to );
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void nbd_r2h_request( struct nbd_request_raw *from, struct nbd_request * to );
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void nbd_r2h_reply( struct nbd_reply_raw * from, struct nbd_reply * to );
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void nbd_h2r_init( struct nbd_init * from, struct nbd_init_raw * to);
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void nbd_h2r_request( struct nbd_request * from, struct nbd_request_raw * to );
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void nbd_h2r_reply( struct nbd_reply * from, struct nbd_reply_raw * to );
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#endif
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