Date: Tue, 6 Jun 2023 14:25:38 +0300 From: Vitaliy Gusev <gusev.vitaliy@gmail.com> To: =?utf-8?Q?Corvin_K=C3=B6hne?= <corvink@FreeBSD.org> Cc: virtualization@freebsd.org, freebsd-hackers@freebsd.org Subject: Re: BHYVE SNAPSHOT image format proposal Message-ID: <8387AC83-6667-48E5-A3FA-11475EA96A5F@gmail.com> In-Reply-To: <6b98da58a5bd8e83bc466efa20b5a900298210aa.camel@FreeBSD.org> References: <67FDC8A8-86A6-4AE4-85F0-FF7BEF9F2F06@gmail.com> <6b98da58a5bd8e83bc466efa20b5a900298210aa.camel@FreeBSD.org>
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[-- Attachment #1 --] Hi Corvin, Thanks for your comments and advices. Answers are below, > On 5 Jun 2023, at 18:32, Corvin Köhne <corvink@FreeBSD.org> wrote: > > On Tue, 2023-05-23 at 19:05 +0300, Vitaliy Gusev wrote: >> 2. HEADER PHYS format: >> >> 0 +—————————————————————————————————————————+ >> | IDENT STRING - 64 BYTES | >> 64 +—————————————————————————————————————————+ >> | NVLIST SIZE - 4 BYTES | NVLIST DATA | >> 72 +—————————————————————————————————————————+ >> | | >> | NVLIST DATA | >> | | >> 4096 +—————————————————————————————————————————+ >> >>> >>> IDENT STRING - Each producer can set its own value to specify >>> image. >>> NVLIST SIZE - The following packed header nvlist data size. >>> NVLIST DATA - Packed nvlist header data. >>> >>> 4KB should be enough for the HEADER to keep basic information about >>> Sections. However, it can >>> be enlarged lately, without breaking backward compatibility. >>> > > I can't see an advantage of using a fixed sized header of 4KB. You have > to parse the offset and size of every section anyways. If it's for > alignment requirements you can still align all sections on save and set > the offset accordingly. So, why complicating things by using a fixed > header size? You are right about 4KB restriction. I will correct it in updated format proposal. Idea is to reserve enough space for HEADER and write it after all finished stages at the beginning of a snapshot file. Implementation (snapshot path) should know estimated maximum size of the header and can use the possible maximum. Currently 4KB is enough and easily can be increased in the bhyve’s code without any problem. Alignment is useful to debug and looking into snapshot image file. > > The IDENT STRING seems to be very large. Even a GUID which should be a > global unique identifier uses just 16 Bytes. Additionally, it might be > worth using a dedicated ident and version field for an easier version > parsing. E.g.: Intention is to add enough space for the future version (as reservation) and other producers and companies to specify it’s own ID string with possible add-on information. So adding 64 bytes for the future is not so huge pay, but can be very useful. During resume, if IDENT string is not the same as in bhyve, resume can fail before parsing other data, because it could be that internal format is not as expected. I would not to fix IDENT string format and just apply rule: During resume, bhyve compares its own IDENT string and IDENT string from an Snapshot image. If it is not the same, further assumption about format cannot be done, and resume should fail. > > +------------------+-------------------+ > | IDENT - 56 BYTES | VERSION - 8 BYTES | > +------------------+-------------------+ > > IDENT - "BHYVE CHECKPOINT IMAGE" > VERSION - 1 (as uint64_t) > > Btw: I don't care but here we could leave some free space for possible > forward compatibility. E.g.: > > +------------------+-------------------+-------------------------+ > | IDENT - 16 BYTES | VERSION - 8 BYTES | _FREE_SPACE_ - 40 BYTES | > +------------------+-------------------+————————————+ ... >> 4. EXAMPLE: >> >> >> IDENT STRING: >> >> "BHYVE CHECKPOINT IMAGE VERSION 1" >> >> NVLIST HEADER: >> >> [config] >> config.offset = 0x1000 (4096) >> config.size = 0x1f6 (502) >> config.type = "text" >> > > Not sure if it's just an example for the "text" type. bhyve converts it > into a nvlist, so it could be saved directly as nvlist. > Btw: I would only implement the "text" type if there's an usecase that > can't be solved by one of the other types. Intention is to use current engine to dump bhyve’s config and read config from a file (-k option). Advantage of using “text” type - simple implementation and as an example of flexibility of proposed image format. Image file can keep any types that a producer would like to use: text, nvlist, binary, diff-pages, etc. > > All in all, it looks good. Keep on your work! > > Regards checksum feature: > We should focus on enabling this feature by default before adding > advanced features. So, keep it simple and small. Could you give a more example what you meant about “checksum” feature? Did you mean as TAR’s checksum, i.e. only header? > > Regards forward compatibility: > Backward compatibility is way more important than forward > compatibility. Nevertheless, forward compatibility would be nice to > have. So, we should keep it in mind when modifying the layout. For the > moment, just focus on a format which is backward compatible. > It seems that having information about forward compatibility could be very useful, at least to get it in advance if it is impossible to restore. I will add it during implementing this format. Thanks, Vitaliy Gusev [-- Attachment #2 --] <html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Hi Corvin, <div><br></div><div>Thanks for your comments and advices. </div><div><br></div><div>Answers are below,<br><div><div><br><blockquote type="cite"><div>On 5 Jun 2023, at 18:32, Corvin Köhne <corvink@FreeBSD.org> wrote:</div><br class="Apple-interchange-newline"><div><meta charset="UTF-8"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">On Tue, 2023-05-23 at 19:05 +0300, Vitaliy Gusev wrote:</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><blockquote type="cite" style="font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">2. HEADER PHYS format: </blockquote><blockquote type="cite" style="font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><br> 0 +—————————————————————————————————————————+ <br> <span class="Apple-converted-space"> </span>| IDENT STRING - 64 BYTES |<br> 64 +—————————————————————————————————————————+ <br> <span class="Apple-converted-space"> </span>| NVLIST SIZE - 4 BYTES | NVLIST DATA |<br> 72 +—————————————————————————————————————————+<br> <span class="Apple-converted-space"> </span>| |<br> <span class="Apple-converted-space"> </span>| NVLIST DATA |<br> <span class="Apple-converted-space"> </span>| |<br> 4096 +—————————————————————————————————————————+<br><br><blockquote type="cite"><br>IDENT STRING - Each producer can set its own value to specify<br>image.<br>NVLIST SIZE - The following packed header nvlist data size.<br>NVLIST DATA - Packed nvlist header data.<br><br>4KB should be enough for the HEADER to keep basic information about<br>Sections. However, it can<br>be enlarged lately, without breaking backward compatibility. <br><br></blockquote></blockquote><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">I can't see an advantage of using a fixed sized header of 4KB. You have</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">to parse the offset and size of every section anyways. If it's for</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">alignment requirements you can still align all sections on save and set</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">the offset accordingly. So, why complicating things by using a fixed</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">header size?</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"></div></blockquote><div><br></div><div>You are right about 4KB restriction. I will correct it in updated format proposal. Idea is</div><div>to reserve enough space for HEADER and write it after all finished stages at the beginning </div><div>of a snapshot file.</div><div><br></div><div>Implementation (snapshot path) should know estimated maximum size of the header and can</div><div>use the possible maximum. Currently 4KB is enough and easily can be</div><div>increased in the bhyve’s code without any problem. </div><div><br></div>Alignment is useful to debug and looking into snapshot image file.</div><div><br><blockquote type="cite"><div><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">The IDENT STRING seems to be very large. Even a GUID which should be a</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">global unique identifier uses just 16 Bytes. Additionally, it might be</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">worth using a dedicated ident and version field for an easier version</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">parsing. E.g.:</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"></div></blockquote><div><br></div><div>Intention is to add enough space for the future version (as reservation) and other producers</div><div>and companies to specify it’s own ID string with possible add-on information. So adding 64 bytes</div><div>for the future is not so huge pay, but can be very useful.</div><div><br></div><div>During resume, if IDENT string is not the same as in bhyve, resume can fail before parsing</div><div>other data, because it could be that internal format is not as expected.</div><div><br></div><div>I would not to fix IDENT string format and just apply rule:</div><div><br></div></div></div></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;"><div><div>During resume, bhyve compares its own IDENT string and IDENT string from an</div><div>Snapshot image. If it is not the same, further assumption about format cannot be done,</div><div>and resume should fail.</div></div></blockquote><div><div><div><br></div><blockquote type="cite"><div><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">+------------------+-------------------+</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">| IDENT - 56 BYTES | VERSION - 8 BYTES |</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">+------------------+-------------------+</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">IDENT - "BHYVE CHECKPOINT IMAGE"</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">VERSION - 1 (as uint64_t)</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">Btw: I don't care but here we could leave some free space for possible</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">forward compatibility. E.g.:</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">+------------------+-------------------+-------------------------+</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">| IDENT - 16 BYTES | VERSION - 8 BYTES | _FREE_SPACE_ - 40 BYTES |</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">+------------------+-------------------+————————————+</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"></div></blockquote>...<br><blockquote type="cite"><div><blockquote type="cite" style="font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">4. EXAMPLE:<br><br><br> IDENT STRING:<br><br> "BHYVE CHECKPOINT IMAGE VERSION 1"<br><br> NVLIST HEADER: <br><br> <span class="Apple-converted-space"> </span>[config]<br> <span class="Apple-converted-space"> </span>config.offset = 0x1000 (4096)<br> <span class="Apple-converted-space"> </span>config.size = 0x1f6 (502)<br> <span class="Apple-converted-space"> </span>config.type = "text"<br><br></blockquote><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">Not sure if it's just an example for the "text" type. bhyve converts it</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">into a nvlist, so it could be saved directly as nvlist.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"></div></blockquote><blockquote type="cite"><div><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">Btw: I would only implement the "text" type if there's an usecase that</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">can't be solved by one of the other types.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"></div></blockquote><div><br></div><div><br></div><div><div>Intention is to use current engine to dump bhyve’s config and read config</div><div>from a file (-k option).</div><div><br></div><div>Advantage of using “text” type - simple implementation and as an example</div><div>of flexibility of proposed image format. Image file can keep any types that</div><div>a producer would like to use: text, nvlist, binary, diff-pages, etc.</div></div><br><blockquote type="cite"><div><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">All in all, it looks good. Keep on your work!</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">Regards checksum feature:</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">We should focus on enabling this feature by default before adding</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">advanced features. So, keep it simple and small.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"></div></blockquote><div><br></div><div>Could you give a more example what you meant about “checksum” feature? Did you mean as</div><div>TAR’s checksum, i.e. only header?</div><div><br></div><br><blockquote type="cite"><div><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">Regards forward compatibility:</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">Backward compatibility is way more important than forward</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">compatibility. Nevertheless, forward compatibility would be nice to</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">have. So, we should keep it in mind when modifying the layout. For the</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">moment, just focus on a format which is backward compatible.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 13.999999px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"></div></blockquote><div><br></div><div>It seems that having information about forward compatibility could be very</div><div>useful, at least to get it in advance if it is impossible to restore. I will add it during</div><div>implementing this format.</div><div><br></div></div><div>Thanks,</div><div>Vitaliy Gusev</div><div><br></div></div></body></html>
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