> For the complete documentation index, see [llms.txt](https://theiotlearninginitiative.gitbook.io/embedded-linux/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://theiotlearninginitiative.gitbook.io/embedded-linux/subsystems/block.md). # Block > Block devices are hardware devices distinguished by the random (that is, not necessarily sequential) access of fixed-size chunks of data, called blocks. The most common block device is a hard disk, but many other block devices exist, such as floppy drives, CD-ROM drives, and flash memory. Notice how these are all devices on which you mount a filesystemfilesystems are the lingua franca of block devices. [Makelinux](http://www.makelinux.net/books/lkd2/ch13) * [Differences between flash devices and block drives](http://www.linux-mtd.infradead.org/faq/general.html#L_mtd_vs_hdd) * [Creating a ram disk on Linux](http://unix.stackexchange.com/questions/66329/creating-a-ram-disk-on-linux) * [Free Electrons Block Drivers](http://free-electrons.com/doc/block_drivers.pdf) ## Kernel Integration ### Kernel Display Message Card Insertion ```bash root@edison:~# dmesg ... [ 4430.481280] mmc1: new high speed SDHC card at address 1234 [ 4430.482221] mmcblk1: mmc1:1234 SA04G 3.63 GiB [ 4430.485107] mmcblk1: p1 ``` ### Kernel Display Message Default ```bash root@edison:~# dmesg | grep mmc [ 0.190762] SDIO bus = 1, name = bcm43xx_clk_vmmc, ref_clock = 26000000, addr =0x401 [ 0.741385] emmc_ipanic: init success [ 1.013752] mmc0: no vqmmc regulator found [ 1.108914] mmc0: BKOPS_EN bit is not set00 [ 1.417542] mmc0: new HS200 MMC card at address 0001 [ 1.418397] mmcblk0: mmc0:0001 H4G1d\x04 3.64 GiB [ 1.418943] mmcblk0boot0: mmc0:0001 H4G1d\x04 partition 1 4.00 MiB [ 1.419442] mmcblk0boot1: mmc0:0001 H4G1d\x04 partition 2 4.00 MiB [ 1.419935] mmcblk0rpmb: mmc0:0001 H4G1d\x04 partition 3 4.00 MiB [ 1.426000] mmcblk0: p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 [ 1.434287] mmcblk0boot1: unknown partition table [ 1.437970] mmcblk0boot0: unknown partition table [ 1.438383] mmc0: SDHCI controller on PCI [0000:00:01.0] using ADMA [ 1.454185] emmc_ipanic: panic partition found, label:panic, device:mmcblk0p6 [ 1.557291] emmc_ipanic: emmc_panic_notify_add: Data available in panic partition [ 1.557341] emmc_ipanic: emmc_panic_notify_add: proc entry created: emmc_ipanic_header [ 1.557362] emmc_ipanic: emmc_panic_notify_add: log file 0(1024, 52340) [ 1.557390] emmc_ipanic: emmc_panic_notify_add: proc entry created: emmc_ipanic_console [ 1.557407] emmc_ipanic: emmc_panic_notify_add: log file 1(4286578688, 0) [ 1.557420] emmc_ipanic: emmc_panic_notify_add: empty log file 1 [ 1.557436] emmc_ipanic: emmc_panic_notify_add: log file 2(4286578688, 0) [ 1.557449] emmc_ipanic: emmc_panic_notify_add: empty log file 2 [ 1.584823] mmc1: no vqmmc regulator found [ 1.585258] mmc1: SDHCI controller on PCI [0000:00:01.2] using ADMA [ 1.586232] mmc2: no vqmmc regulator found [ 1.586668] mmc2: SDHCI controller on PCI [0000:00:01.3] using ADMA [ 1.746719] EXT4-fs (mmcblk0p8): INFO: recovery required on readonly filesystem [ 1.746745] EXT4-fs (mmcblk0p8): write access will be enabled during recovery [ 1.819782] mmc1: error -84 whilst initialising SD card [ 1.831504] EXT4-fs (mmcblk0p8): recovery complete [ 1.834101] EXT4-fs (mmcblk0p8): mounted filesystem with ordered data mode. Opts: (null) [ 1.897473] mmc1: new high speed SDHC card at address 1234 [ 1.898207] mmcblk1: mmc1:1234 SA08G 7.21 GiB [ 1.899941] mmcblk1: p1 p2 [ 2.226457] mmc2: queuing unknown CIS tuple 0x91 (3 bytes) [ 2.226495] mmc2: new ultra high speed DDR50 SDIO card at address 0001 [ 4.543403] bcmsdh_sdmmc: bcmsdh_sdmmc_probe Enter [ 4.543666] bcmsdh_sdmmc: bcmsdh_sdmmc_probe Enter [ 4.567337] bcmsdh_sdmmc: bcmsdh_sdmmc_probe Enter [ 5.453381] EXT4-fs (mmcblk0p8): re-mounted. Opts: (null) [ 5.965905] lun0: LUN: file: /dev/mmcblk0p9 [ 8.512646] FAT-fs (mmcblk0p7): Volume was not properly unmounted. Some data may be corrupt. Please run fsck. [ 8.557697] EXT4-fs (mmcblk0p10): mounted filesystem with ordered data mode. Opts: (null) ``` ## Applications / Libraries ### Setup #### Opkg ```bash root@edison:~# opkg update root@edison:~# opkg install e2fsprogs dosfstools ``` #### Apt-Get ```bash root@edison:~# apt-get update root@edison:~# apt-get install e2fsprogs dosfstools xfsprogs ``` ### Programs #### Mount ```bash root@edison:~# mount /dev/mmcblk0p8 on / type ext4 (rw,nodev,noatime,discard,noauto_da_alloc,data=ordered) ... /dev/mmcblk0p7 on /boot type vfat (rw,nosuid,nodev,noatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortna) /dev/mmcblk1p1 on /media/sdcard type ext3 (rw,relatime,errors=continue,user_xattr,acl,barrier=1,data=writeback) ``` ### Usage Models #### SD Cards, Mount ```bash root@edison:~# mount /dev/mmcblk0p7 on /boot type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,err) /dev/mmcblk0p10 on /home type ext4 (rw,relatime,data=ordered) /dev/mmcblk1p1 on /media/sdcard type vfat (rw,relatime,uid=65534,fmask=0000,dmask=0000,allow_utime=0022,codepage=437,ioch) root@edison:~# mkfs.ext4 /dev/mmcblk1 mke2fs 1.42.9 (28-Dec-2013) /dev/mmcblk1 is apparently in use by the system; will not make a filesystem here! root@edison:~# umount root@edison:~# umount /media/sdcard/ root@edison:~# mkfs.ext4 /dev/mmcblk1 mke2fs 1.42.9 (28-Dec-2013) Discarding device blocks: done Filesystem label= OS type: Linux Block size=4096 (log=2) ... Creating journal (16384 blocks): done Writing superblocks and filesystem accounting information: done root@edison:~# mkfs.ext4 -t ext4 /dev/mmcblk1 ``` #### SD Cards, Manual Mount ```bash root@edison:~# mkdir localdirectory root@edison:~# mount -t ext4 /dev/mmcblk1 localdirectory root@edison:~# mount | grep mmcblk1 ... /dev/mmcblk1 on /root/localdirectory type ext4 (rw,relatime,data=ordered) root@edison:~# cd localdirectory/ root@edison:~/localdirectory# ls lost+found root@edison:~/localdirectory# ``` #### SD Cards, Umount ```bash root@edison:~# umount localdirectory root@edison:~# umount /dev/mmcblk1 ``` #### SD Cards, Automatic Mount ```bash root@edison:~# vi /etc/fstab /dev/mmcblk1 /path/to/localdirectory ``` #### Tmpfs > tmpfs is a common name for a temporary file storage facility on many Unix-like operating systems. It is intended to appear as a mounted file system, but stored in volatile memory instead of a persistent storage device. [Wikipedia](https://en.wikipedia.org/wiki/Tmpfs) ```bash root@edison:~# cd /tmp root@edison:~# mkdir temptmpfs root@edison:~# mount -o size=16G -t tmpfs none temptmpfs/ root@edison:~# cd temptmpfs/ root@edison:~# ls root@edison:~# cd .. root@edison:~# mount ... none on /root/temptmpfs type tmpfs (rw,relatime,size=16777216k) root@edison:~# umount /root/temptmpfs ``` --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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