linux-kernel - Re: [PATCH] sd: close hole in > 2T device rejection when !CONFIG

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Date:   Tue, 04 Apr 2017 19:35:05 -0400
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     Bart Van Assche <Bart.VanAssche@...disk.com>
Cc:     "jejb\@linux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>,
        "steve.magnani\@digidescorp.com" <steve.magnani@...idescorp.com>,
        "martin.petersen\@oracle.com" <martin.petersen@...cle.com>,
        "linux-scsi\@vger.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "steve\@digidescorp.com" <steve@...idescorp.com>
Subject: Re: [PATCH] sd: close hole in > 2T device rejection when !CONFIG_LBDAF

Bart Van Assche <Bart.VanAssche@...disk.com> writes:

Hi Bart,

> Sorry but I still don't understand why the two checks are
> different. How about the (untested) patch below? The approach below
> avoids that the check is duplicated and - at least in my opinion -
> results in code that is easier to read.

Just tripped over this issue in connection with something else. However,
I had to make a few passes to convince myself that your proposed fix was
correct. How about something like the following?

Martin

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index fb9b4d29af0b..6084c415c070 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2102,6 +2102,16 @@ static void read_capacity_error(struct scsi_disk *sdkp, struct scsi_device *sdp,
 
 #define READ_CAPACITY_RETRIES_ON_RESET	10
 
+static bool sd_addressable_capacity(u64 lba, unsigned int sector_size)
+{
+	u64 last_sector = lba + 1ULL << ilog2(sector_size) - 9;
+
+	if (sizeof(sector_t) == 4 && last_sector > 0xffffffffULL)
+		return false;
+
+	return true;
+}
+
 static int read_capacity_16(struct scsi_disk *sdkp, struct scsi_device *sdp,
 						unsigned char *buffer)
 {
@@ -2167,7 +2177,7 @@ static int read_capacity_16(struct scsi_disk *sdkp, struct scsi_device *sdp,
 		return -ENODEV;
 	}
 
-	if ((sizeof(sdkp->capacity) == 4) && (lba >= 0xffffffffULL)) {
+	if (!sd_addressable_capacity(lba, sector_size)) {
 		sd_printk(KERN_ERR, sdkp, "Too big for this kernel. Use a "
 			"kernel compiled with support for large block "
 			"devices.\n");
@@ -2256,7 +2266,7 @@ static int read_capacity_10(struct scsi_disk *sdkp, struct scsi_device *sdp,
 		return sector_size;
 	}
 
-	if ((sizeof(sdkp->capacity) == 4) && (lba == 0xffffffff)) {
+	if (!sd_addressable_capacity(lba, sector_size)) {
 		sd_printk(KERN_ERR, sdkp, "Too big for this kernel. Use a "
 			"kernel compiled with support for large block "
 			"devices.\n");