loop: optionally use ioctl(LOOP_CONFIGURE) to set up loopdevs

LOOP_CONFIGURE is added to Linux 5.8 function old new delta NO_LOOP_CONFIGURE (old code): set_loop 784 782 -2 LOOP_CONFIGURE: set_loop 784 653 -131 TRY_LOOP_CONFIGURE: set_loop 784 811 +27 Based on a patch by Xiaoming Ni <nixiaoming@huawei.com> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
author: Denys Vlasenko <vda.linux@googlemail.com> 2022-12-13 14:27:08 +0100
committer: Denys Vlasenko <vda.linux@googlemail.com> 2022-12-13 15:21:28 +0100
commit: 45734a23515b3e1f2305ad33dc22d1bc69e3cba6 (patch)
tree: 5527d42c4853823b4002a837aabe0d025343ff79 /libbb
parent: 9df54deead6845fc38509c412736b47a9a5d5187 (diff)
download: busybox-w32-45734a23515b3e1f2305ad33dc22d1bc69e3cba6.tar.gz
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2 files changed, 65 insertions, 9 deletions
diff --git a/libbb/Config.src b/libbb/Config.src
index 66a3ffa23..b980f19a9 100644
--- a/libbb/Config.src
+++ b/libbb/Config.src
@@ -369,3 +369,25 @@ config UNICODE_PRESERVE_BROKEN
        For example, this means that entering 'l', 's', ' ', 0xff, [Enter]
        at shell prompt will list file named 0xff (single char name
        with char value 255), not file named '?'.
+choice
+        prompt "Use LOOP_CONFIGURE for losetup and loop mounts"
+        default TRY_LOOP_CONFIGURE
+        help
+        LOOP_CONFIGURE is added to Linux 5.8
+        https://lwn.net/Articles/820408/
+        This allows userspace to completely setup a loop device with a single
+        ioctl, removing the in-between state where the device can be partially
+        configured - eg the loop device has a backing file associated with it,
+        but is reading from the wrong offset.
+config LOOP_CONFIGURE
+        bool "use LOOP_CONFIGURE, needs kernel >= 5.8"
+config NO_LOOP_CONFIGURE
+        bool "use LOOP_SET_FD + LOOP_SET_STATUS"
+config TRY_LOOP_CONFIGURE
+        bool "try LOOP_CONFIGURE, fall back to LOOP_SET_FD + LOOP_SET_STATUS"
+endchoice
diff --git a/libbb/loop.c b/libbb/loop.c
index 424c39216..e930b1b1f 100644
--- a/libbb/loop.c
+++ b/libbb/loop.c
@@ -110,26 +110,39 @@ static int get_next_free_loop(char *dev, int id)
        return loopdevno;
 }
-static int set_loopdev_params(int ffd,
+#if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE
-                int lfd, const char *file,
+# define LOOP_CONFIGURE 0x4C0A
+struct loop_config {
+        uint32_t fd;
+        uint32_t block_size;
+        struct loop_info64 info;
+        uint64_t __reserved[8];
+};
+#endif
+static int set_loopdev_params(int lfd,
+                int ffd, const char *file,
                unsigned long long offset,
                unsigned long long sizelimit,
                unsigned flags)
 {
        int rc;
+#if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE
+        struct loop_config lconfig;
+# define loopinfo lconfig.info
+#else
        bb_loop_info loopinfo;
+#endif
        rc = ioctl(lfd, BB_LOOP_GET_STATUS, &loopinfo);
        /* If device is free, try to claim it */
        if (rc && errno == ENXIO) {
-                /* Associate free loop device with file */
+#if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE
-                rc = ioctl(lfd, LOOP_SET_FD, ffd);
+                memset(&lconfig, 0, sizeof(lconfig));
-                if (rc != 0) {
+#else
-                        /* Ouch... race: the device already has a fd */
-                        return -1;
-                }
                memset(&loopinfo, 0, sizeof(loopinfo));
+#endif
                safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE);
                loopinfo.lo_offset = offset;
                loopinfo.lo_sizelimit = sizelimit;
@@ -140,6 +153,25 @@ static int set_loopdev_params(int ffd,
                 * is wrong (would free the loop device!)
                 */
                loopinfo.lo_flags = (flags & ~BB_LO_FLAGS_READ_ONLY);
+#if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_LOOP_CONFIGURE
+                lconfig.fd = ffd;
+                rc = ioctl(lfd, LOOP_CONFIGURE, &lconfig);
+                if (rc == 0)
+                        return rc; /* SUCCESS! */
+# if ENABLE_TRY_LOOP_CONFIGURE
+                if (errno != EINVAL)
+                        return rc; /* error other than old kernel */
+                /* Old kernel, fall through into old way to do it: */
+# endif
+#endif
+#if ENABLE_TRY_LOOP_CONFIGURE || ENABLE_NO_LOOP_CONFIGURE
+                /* Associate free loop device with file */
+                rc = ioctl(lfd, LOOP_SET_FD, ffd);
+                if (rc != 0) {
+                        /* Ouch... race: the device already has a fd */
+                        return rc;
+                }
                rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo);
                if (rc != 0 && (loopinfo.lo_flags & BB_LO_FLAGS_AUTOCLEAR)) {
                        /* Old kernel, does not support LO_FLAGS_AUTOCLEAR? */
@@ -151,8 +183,10 @@ static int set_loopdev_params(int ffd,
                        return rc; /* SUCCESS! */
                /* failure, undo LOOP_SET_FD */
                ioctl(lfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary
+#endif
        }
        return -1;
+#undef loopinfo
 }
 /* Returns opened fd to the loop device, <0 on error.
@@ -227,7 +261,7 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
                        goto try_next_loopN;
                }
-                rc = set_loopdev_params(ffd, lfd, file, offset, sizelimit, flags);
+                rc = set_loopdev_params(lfd, ffd, file, offset, sizelimit, flags);
                if (rc == 0) {
                        /* SUCCESS! */
                        if (!*device)
author	Denys Vlasenko <vda.linux@googlemail.com>	2022-12-13 14:27:08 +0100
committer	Denys Vlasenko <vda.linux@googlemail.com>	2022-12-13 15:21:28 +0100
commit	45734a23515b3e1f2305ad33dc22d1bc69e3cba6 (patch)
tree	5527d42c4853823b4002a837aabe0d025343ff79 /libbb
parent	9df54deead6845fc38509c412736b47a9a5d5187 (diff)
download	busybox-w32-45734a23515b3e1f2305ad33dc22d1bc69e3cba6.tar.gz busybox-w32-45734a23515b3e1f2305ad33dc22d1bc69e3cba6.tar.bz2 busybox-w32-45734a23515b3e1f2305ad33dc22d1bc69e3cba6.zip

diff --git a/libbb/Config.src b/libbb/Config.src index 66a3ffa23..b980f19a9 100644 --- a/libbb/Config.src +++ b/libbb/Config.src
@@ -369,3 +369,25 @@ config UNICODE_PRESERVE_BROKEN
369	For example, this means that entering 'l', 's', ' ', 0xff, [Enter]	369	For example, this means that entering 'l', 's', ' ', 0xff, [Enter]
370	at shell prompt will list file named 0xff (single char name	370	at shell prompt will list file named 0xff (single char name
371	with char value 255), not file named '?'.	371	with char value 255), not file named '?'.
		372
		373	choice
		374	prompt "Use LOOP_CONFIGURE for losetup and loop mounts"
		375	default TRY_LOOP_CONFIGURE
		376	help
		377	LOOP_CONFIGURE is added to Linux 5.8
		378	https://lwn.net/Articles/820408/
		379	This allows userspace to completely setup a loop device with a single
		380	ioctl, removing the in-between state where the device can be partially
		381	configured - eg the loop device has a backing file associated with it,
		382	but is reading from the wrong offset.
		383
		384	config LOOP_CONFIGURE
		385	bool "use LOOP_CONFIGURE, needs kernel >= 5.8"
		386
		387	config NO_LOOP_CONFIGURE
		388	bool "use LOOP_SET_FD + LOOP_SET_STATUS"
		389
		390	config TRY_LOOP_CONFIGURE
		391	bool "try LOOP_CONFIGURE, fall back to LOOP_SET_FD + LOOP_SET_STATUS"
		392
		393	endchoice


diff --git a/libbb/loop.c b/libbb/loop.c index 424c39216..e930b1b1f 100644 --- a/libbb/loop.c +++ b/libbb/loop.c
@@ -110,26 +110,39 @@ static int get_next_free_loop(char *dev, int id)
110	return loopdevno;	110	return loopdevno;
111	}	111	}
112		112
113	static int set_loopdev_params(int ffd,	113	#if ENABLE_TRY_LOOP_CONFIGURE \|\| ENABLE_LOOP_CONFIGURE
114	int lfd, const char *file,	114	# define LOOP_CONFIGURE 0x4C0A
		115	struct loop_config {
		116	uint32_t fd;
		117	uint32_t block_size;
		118	struct loop_info64 info;
		119	uint64_t __reserved[8];
		120	};
		121	#endif
		122
		123	static int set_loopdev_params(int lfd,
		124	int ffd, const char *file,
115	unsigned long long offset,	125	unsigned long long offset,
116	unsigned long long sizelimit,	126	unsigned long long sizelimit,
117	unsigned flags)	127	unsigned flags)
118	{	128	{
119	int rc;	129	int rc;
		130	#if ENABLE_TRY_LOOP_CONFIGURE \|\| ENABLE_LOOP_CONFIGURE
		131	struct loop_config lconfig;
		132	# define loopinfo lconfig.info
		133	#else
120	bb_loop_info loopinfo;	134	bb_loop_info loopinfo;
		135	#endif
121		136
122	rc = ioctl(lfd, BB_LOOP_GET_STATUS, &loopinfo);	137	rc = ioctl(lfd, BB_LOOP_GET_STATUS, &loopinfo);
123		138
124	/* If device is free, try to claim it */	139	/* If device is free, try to claim it */
125	if (rc && errno == ENXIO) {	140	if (rc && errno == ENXIO) {
126	/* Associate free loop device with file */	141	#if ENABLE_TRY_LOOP_CONFIGURE \|\| ENABLE_LOOP_CONFIGURE
127	rc = ioctl(lfd, LOOP_SET_FD, ffd);	142	memset(&lconfig, 0, sizeof(lconfig));
128	if (rc != 0) {	143	#else
129	/* Ouch... race: the device already has a fd */
130	return -1;
131	}
132	memset(&loopinfo, 0, sizeof(loopinfo));	144	memset(&loopinfo, 0, sizeof(loopinfo));
		145	#endif
133	safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE);	146	safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE);
134	loopinfo.lo_offset = offset;	147	loopinfo.lo_offset = offset;
135	loopinfo.lo_sizelimit = sizelimit;	148	loopinfo.lo_sizelimit = sizelimit;
@@ -140,6 +153,25 @@ static int set_loopdev_params(int ffd,
140	* is wrong (would free the loop device!)	153	* is wrong (would free the loop device!)
141	*/	154	*/
142	loopinfo.lo_flags = (flags & ~BB_LO_FLAGS_READ_ONLY);	155	loopinfo.lo_flags = (flags & ~BB_LO_FLAGS_READ_ONLY);
		156
		157	#if ENABLE_TRY_LOOP_CONFIGURE \|\| ENABLE_LOOP_CONFIGURE
		158	lconfig.fd = ffd;
		159	rc = ioctl(lfd, LOOP_CONFIGURE, &lconfig);
		160	if (rc == 0)
		161	return rc; /* SUCCESS! */
		162	# if ENABLE_TRY_LOOP_CONFIGURE
		163	if (errno != EINVAL)
		164	return rc; /* error other than old kernel */
		165	/* Old kernel, fall through into old way to do it: */
		166	# endif
		167	#endif
		168	#if ENABLE_TRY_LOOP_CONFIGURE \|\| ENABLE_NO_LOOP_CONFIGURE
		169	/* Associate free loop device with file */
		170	rc = ioctl(lfd, LOOP_SET_FD, ffd);
		171	if (rc != 0) {
		172	/* Ouch... race: the device already has a fd */
		173	return rc;
		174	}
143	rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo);	175	rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo);
144	if (rc != 0 && (loopinfo.lo_flags & BB_LO_FLAGS_AUTOCLEAR)) {	176	if (rc != 0 && (loopinfo.lo_flags & BB_LO_FLAGS_AUTOCLEAR)) {
145	/* Old kernel, does not support LO_FLAGS_AUTOCLEAR? */	177	/* Old kernel, does not support LO_FLAGS_AUTOCLEAR? */
@@ -151,8 +183,10 @@ static int set_loopdev_params(int ffd,
151	return rc; /* SUCCESS! */	183	return rc; /* SUCCESS! */
152	/* failure, undo LOOP_SET_FD */	184	/* failure, undo LOOP_SET_FD */
153	ioctl(lfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary	185	ioctl(lfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary
		186	#endif
154	}	187	}
155	return -1;	188	return -1;
		189	#undef loopinfo
156	}	190	}
157		191
158	/* Returns opened fd to the loop device, <0 on error.	192	/* Returns opened fd to the loop device, <0 on error.
@@ -227,7 +261,7 @@ int FAST_FUNC set_loop(char *device, const char file, unsigned long long offse
227	goto try_next_loopN;	261	goto try_next_loopN;
228	}	262	}
229		263
230	rc = set_loopdev_params(ffd, lfd, file, offset, sizelimit, flags);	264	rc = set_loopdev_params(lfd, ffd, file, offset, sizelimit, flags);
231	if (rc == 0) {	265	if (rc == 0) {
232	/* SUCCESS! */	266	/* SUCCESS! */
233	if (!*device)	267	if (!*device)