TARG(4)

💖 TARG(4) — SCSI target emulator driver 💖

okay bestie, sit down, we're learning about targ from the Kernel Interfaces Manual, and honestly? it's giving main character energy. ✨

---

🌸 NAME 🌸

targ — the SCSI target emulator driver. yes that's it, that's the whole name, slay. 💅

---

🦋 SYNOPSIS 🦋

so if you wanna compile this driver into the kernel (no cap, it's a kernel-config situation), you drop this line into your kernel configuration file:

device targ

that's the whole thing. iconic. 🎀

---

✨ DESCRIPTION ✨

okay so here's the tea: the targ driver gives usermode programs an interface to emulate SCSI target devices. and if you want a whole example of it doing its thing, there's a sample program that emulates a disk drive — lowkey similar to da(4) — living right here: /usr/share/examples/scsi_target. go look, it's right there. 🫶

the targ driver hands you the control device /dev/targ. so the flow is:

1. you open the device 🔓
2. the file descriptor has to be bound to a specific bus/target/LUN and enabled to process CCBs — that's the TARGIOCENABLE ioctl doing the work
3. then your process uses write(2) to send CCBs over to the SIM
4. and poll(2) or kqueue(2) to check if responses are ready 👀
5. pointers to completed CCBs come back to you via read(2)
6. and any data transfers the user CCBs asked for? done via zero-copy IO. periodt. 🔥

---

💅 IOCTLS 💅

these ioctl(2) calls are all defined in the header file <cam/scsi/scsi_targetio.h>. let's go one by one, bestie:

• TARGIOCENABLE — (struct ioc_enable_lun) — this one enables target mode on the LUN you specify. and you specify it with this structure right here:

struct ioc_enable_lun {
        path_id_t       path_id;
        target_id_t     target_id;
        lun_id_t        lun_id;
        int             grp6_len;
        int             grp7_len;
};

🚨 important: the selected path (bus), target, and LUN must not already be in use, or you get EADDRINUSE back. no sharing, babe.

and if grp6_len or grp7_len are non-zero, then reception of vendor-specific commands is enabled. cute little bonus. ✨

• TARGIOCDISABLE — disables target mode and aborts all pending CCBs. the CCBs may optionally be read as they complete, if you want. after that you can call TARGIOCENABLE again to activate a different LUN. multiple disable calls have no effect (it's not gonna get more disabled, bestie). and btw, the close(2) system call automatically disables target mode if it's enabled — so you don't even have to ask. 💜
• TARGIOCDEBUG — (int) — enables CAM_PERIPH debugging if the argument is non-zero, otherwise it disables it. that's it. flip the switch. 🎚️

---

🍓 FILES 🍓

• <cam/scsi/scsi_targetio.h> — describes the usermode interface.
• /sys/cam/scsi/scsi_target.c — is the driver source file.
• /dev/targ — is the control device.

---

🌈 SEE ALSO 🌈

• /usr/share/examples/scsi_target
• ahc(4)
• isp(4)
• scsi(4)
• FreeBSD Target Information, http://www.root.org/~nate/freebsd/

---

👑 AUTHORS 👑

the targ driver first appeared in FreeBSD 3.0 and was written by Justin T. Gibbs. then it got rewritten for FreeBSD 5.0 by Nate Lawson <nate@root.org>. glow-up era fr fr. 💖

---

💀 BUGS 💀

okay so the fine print, and we keep it real here:

• Currently, only the ahc(4) and isp(4) drivers fully support target mode. so like… keep that in mind. 😭
• The ahc(4) driver does not support tagged queuing in target mode. not a vibe, but it is the truth.

---

🎀 and that's the whole page, bestie — this manual came to you from Debian, dated December 13, 2011. literally vintage, and still eating. bye mwah 💅🦋✨