From: "Philippe Mathieu-Daudé" <f4bug@amsat.org> To: Markus Armbruster <armbru@redhat.com> Cc: peter.maydell@linaro.org, bin.meng@windriver.com, mark.cave-ayland@ilande.co.uk, qemu-devel@nongnu.org, sundeep.lkml@gmail.com, qemu-block@nongnu.org, andrew.smirnov@gmail.com, hskinnemoen@google.com, joel@jms.id.au, atar4qemu@gmail.com, alistair@alistair23.me, b.galvani@gmail.com, nieklinnenbank@gmail.com, qemu-arm@nongnu.org, clg@kaod.org, kwolf@redhat.com, qemu-riscv@nongnu.org, andrew@aj.id.au, Andrew.Baumann@microsoft.com, jcd@tribudubois.net, kfting@nuvoton.com, hreitz@redhat.com, palmer@dabbelt.com Subject: Re: [PATCH RFC 2/2] hw: Replace drive_get_next() by drive_get() Date: Mon, 15 Nov 2021 22:15:12 +0100 [thread overview] Message-ID: <b18519f7-7198-0965-a528-2d1a45c7c93c@amsat.org> (raw) In-Reply-To: <87lf1pfm2z.fsf@dusky.pond.sub.org> On 11/15/21 16:57, Markus Armbruster wrote: > Philippe Mathieu-Daudé <f4bug@amsat.org> writes: >> On 11/15/21 13:55, Markus Armbruster wrote: >>> drive_get_next() is basically a bad idea. It returns the "next" block >>> backend of a certain interface type. "Next" means bus=0,unit=N, where >>> subsequent calls count N up from zero, per interface type. >>> >>> This lets you define unit numbers implicitly by execution order. If the >>> order changes, or new calls appear "in the middle", unit numbers change. >>> ABI break. Hard to spot in review. >>> >>> Explicit is better than implicit: use drive_get() directly. >>> >>> Signed-off-by: Markus Armbruster <armbru@redhat.com> >>> --- >>> @@ -435,11 +438,13 @@ static void aspeed_machine_init(MachineState *machine) >>> } >>> >>> for (i = 0; i < bmc->soc.sdhci.num_slots; i++) { >>> - sdhci_attach_drive(&bmc->soc.sdhci.slots[i], drive_get_next(IF_SD)); >>> + sdhci_attach_drive(&bmc->soc.sdhci.slots[i], >>> + drive_get(IF_SD, 0, i)); >> >> If we put SD on bus #0, ... >> >>> } >>> >>> if (bmc->soc.emmc.num_slots) { >>> - sdhci_attach_drive(&bmc->soc.emmc.slots[0], drive_get_next(IF_SD)); >>> + sdhci_attach_drive(&bmc->soc.emmc.slots[0], >>> + drive_get(IF_SD, 0, bmc->soc.sdhci.num_slots)); >> >> ... we'd want to put eMMC on bus #1 > > Using separate buses for different kinds of devices would be neater, but > it also would be an incompatible change. This patch keeps existing > bus/unit numbers working. drive_get_next() can only use bus 0. > >> but I see having eMMC cards on a >> IF_SD bus as a bug, since these cards are soldered on the board. > > IF_SD is not a bus, it's an "block interface type", which is really just > a user interface thing. Why are we discriminating by "block interface type" then? What is the difference between "block interfaces"? I see a block drive as a generic unit, usable on multiple hardware devices. I never really understood how this "block interface type" helps developers and users. I thought BlockInterfaceType and DriveInfo were legacy / deprecated APIs we want to get rid of; and we would come up with a replacement API using BlockDeviceInfo or providing a BlockFrontend state of the art object. Anyway, I suppose the explanation is buried in the git history before the last 8 years. I need to keep reading.
WARNING: multiple messages have this Message-ID (diff)
From: "Philippe Mathieu-Daudé" <f4bug@amsat.org> To: Markus Armbruster <armbru@redhat.com> Cc: peter.maydell@linaro.org, bin.meng@windriver.com, mark.cave-ayland@ilande.co.uk, qemu-devel@nongnu.org, jcd@tribudubois.net, qemu-block@nongnu.org, andrew.smirnov@gmail.com, hskinnemoen@google.com, joel@jms.id.au, atar4qemu@gmail.com, alistair@alistair23.me, b.galvani@gmail.com, nieklinnenbank@gmail.com, qemu-arm@nongnu.org, clg@kaod.org, kwolf@redhat.com, qemu-riscv@nongnu.org, andrew@aj.id.au, Andrew.Baumann@microsoft.com, sundeep.lkml@gmail.com, kfting@nuvoton.com, hreitz@redhat.com, palmer@dabbelt.com Subject: Re: [PATCH RFC 2/2] hw: Replace drive_get_next() by drive_get() Date: Mon, 15 Nov 2021 22:15:12 +0100 [thread overview] Message-ID: <b18519f7-7198-0965-a528-2d1a45c7c93c@amsat.org> (raw) In-Reply-To: <87lf1pfm2z.fsf@dusky.pond.sub.org> On 11/15/21 16:57, Markus Armbruster wrote: > Philippe Mathieu-Daudé <f4bug@amsat.org> writes: >> On 11/15/21 13:55, Markus Armbruster wrote: >>> drive_get_next() is basically a bad idea. It returns the "next" block >>> backend of a certain interface type. "Next" means bus=0,unit=N, where >>> subsequent calls count N up from zero, per interface type. >>> >>> This lets you define unit numbers implicitly by execution order. If the >>> order changes, or new calls appear "in the middle", unit numbers change. >>> ABI break. Hard to spot in review. >>> >>> Explicit is better than implicit: use drive_get() directly. >>> >>> Signed-off-by: Markus Armbruster <armbru@redhat.com> >>> --- >>> @@ -435,11 +438,13 @@ static void aspeed_machine_init(MachineState *machine) >>> } >>> >>> for (i = 0; i < bmc->soc.sdhci.num_slots; i++) { >>> - sdhci_attach_drive(&bmc->soc.sdhci.slots[i], drive_get_next(IF_SD)); >>> + sdhci_attach_drive(&bmc->soc.sdhci.slots[i], >>> + drive_get(IF_SD, 0, i)); >> >> If we put SD on bus #0, ... >> >>> } >>> >>> if (bmc->soc.emmc.num_slots) { >>> - sdhci_attach_drive(&bmc->soc.emmc.slots[0], drive_get_next(IF_SD)); >>> + sdhci_attach_drive(&bmc->soc.emmc.slots[0], >>> + drive_get(IF_SD, 0, bmc->soc.sdhci.num_slots)); >> >> ... we'd want to put eMMC on bus #1 > > Using separate buses for different kinds of devices would be neater, but > it also would be an incompatible change. This patch keeps existing > bus/unit numbers working. drive_get_next() can only use bus 0. > >> but I see having eMMC cards on a >> IF_SD bus as a bug, since these cards are soldered on the board. > > IF_SD is not a bus, it's an "block interface type", which is really just > a user interface thing. Why are we discriminating by "block interface type" then? What is the difference between "block interfaces"? I see a block drive as a generic unit, usable on multiple hardware devices. I never really understood how this "block interface type" helps developers and users. I thought BlockInterfaceType and DriveInfo were legacy / deprecated APIs we want to get rid of; and we would come up with a replacement API using BlockDeviceInfo or providing a BlockFrontend state of the art object. Anyway, I suppose the explanation is buried in the git history before the last 8 years. I need to keep reading.
next prev parent reply other threads:[~2021-11-15 21:16 UTC|newest] Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-11-15 12:55 [PATCH RFC 0/2] Eliminate drive_get_next() Markus Armbruster 2021-11-15 12:55 ` Markus Armbruster 2021-11-15 12:55 ` [PATCH RFC 1/2] hw/sd/ssi-sd: Do not create SD card within controller's realize Markus Armbruster 2021-11-15 12:55 ` Markus Armbruster 2021-11-15 13:40 ` Peter Maydell 2021-11-15 13:40 ` Peter Maydell 2021-11-15 13:48 ` Markus Armbruster 2021-11-15 13:48 ` Markus Armbruster 2021-11-15 12:55 ` [PATCH RFC 2/2] hw: Replace drive_get_next() by drive_get() Markus Armbruster 2021-11-15 12:55 ` Markus Armbruster 2021-11-15 13:38 ` Peter Maydell 2021-11-15 13:38 ` Peter Maydell 2021-11-15 13:48 ` Markus Armbruster 2021-11-15 13:48 ` Markus Armbruster 2021-11-15 13:59 ` Philippe Mathieu-Daudé 2021-11-15 13:59 ` Philippe Mathieu-Daudé 2021-11-15 15:57 ` Markus Armbruster 2021-11-15 15:57 ` Markus Armbruster 2021-11-15 21:15 ` Philippe Mathieu-Daudé [this message] 2021-11-15 21:15 ` Philippe Mathieu-Daudé 2021-11-16 7:47 ` Markus Armbruster 2021-11-16 7:47 ` Markus Armbruster 2021-11-16 8:52 ` Cédric Le Goater 2021-11-16 8:52 ` Cédric Le Goater 2021-11-16 9:29 ` Markus Armbruster 2021-11-16 9:29 ` Markus Armbruster 2021-11-16 12:14 ` Cédric Le Goater 2021-11-16 12:14 ` Cédric Le Goater 2021-11-15 14:05 ` [PATCH RFC 0/2] Eliminate drive_get_next() Peter Maydell 2021-11-15 14:05 ` Peter Maydell 2021-11-15 16:01 ` Markus Armbruster 2021-11-15 16:01 ` Markus Armbruster
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