lib: [loopdev.c] cleanup flags usage

Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/include/loopdev.h b/include/loopdev.h
index 74b9e02ecca5ca0366aa5037813e4f996aac37de..a8cb4441b21ed0cf43017325d7c33a25c3fe5d24 100644 (file)
--- a/include/loopdev.h
+++ b/include/loopdev.h
@@ -1,6 +1,8 @@
 #ifndef UTIL_LINUX_LOOPDEV_H
 #define UTIL_LINUX_LOOPDEV_H
 
+#include "sysfs.h"
+
 /*
  * loop_info.lo_encrypt_type
  */
@@ -81,6 +83,7 @@ struct loopdev_cxt {
        char            device[128];    /* device path (e.g. /dev/loop<N>) */
        char            *filename;      /* backing file for loopcxt_set_... */
        int             fd;             /* open(/dev/looo<N>) */
+       int             mode;           /* fd mode O_{RDONLY,RDWR} */
 
        int             flags;          /* LOOPDEV_FL_* flags */
        int             has_info:1;     /* .info contains data */
@@ -95,7 +98,7 @@ struct loopdev_cxt {
  * loopdev_cxt.flags
  */
 enum {
-       LOOPDEV_FL_RDONLY       = (1 << 0),     /* default */
+       LOOPDEV_FL_RDONLY       = (1 << 0),     /* open(/dev/loop) mode; default */
        LOOPDEV_FL_RDWR         = (1 << 1),     /* necessary for loop setup only */
        LOOPDEV_FL_OFFSET       = (1 << 4),
        LOOPDEV_FL_NOSYSFS      = (1 << 5),
@@ -126,7 +129,9 @@ extern int loopcxt_set_device(struct loopdev_cxt *lc, const char *device);
 extern char *loopcxt_strdup_device(struct loopdev_cxt *lc);
 extern const char *loopcxt_get_device(struct loopdev_cxt *lc);
 extern struct sysfs_cxt *loopcxt_get_sysfs(struct loopdev_cxt *lc);
+
 extern int loopcxt_get_fd(struct loopdev_cxt *lc);
+extern int loopcxt_set_fd(struct loopdev_cxt *lc, int fd, int mode);
 
 extern int loopcxt_init_iterator(struct loopdev_cxt *lc, int flags);
 extern int loopcxt_deinit_iterator(struct loopdev_cxt *lc);
@@ -147,6 +152,7 @@ extern char *loopcxt_get_backing_file(struct loopdev_cxt *lc);
 extern int loopcxt_get_offset(struct loopdev_cxt *lc, uint64_t *offset);
 extern int loopcxt_get_sizelimit(struct loopdev_cxt *lc, uint64_t *size);
 extern int loopcxt_is_autoclear(struct loopdev_cxt *lc);
+extern int loopcxt_is_readonly(struct loopdev_cxt *lc);
 extern int loopcxt_find_by_backing_file(struct loopdev_cxt *lc,
                                const char *filename,
                                 uint64_t offset, int flags);

diff --git a/lib/loopdev.c b/lib/loopdev.c
index 9b0d8ba769a2d66c96fc46dbf37104dccd53f9e8..213063b7f29f79ad2acb9670d118f16133e8a18a 100644 (file)
--- a/lib/loopdev.c
+++ b/lib/loopdev.c
@@ -59,8 +59,10 @@ int loopcxt_set_device(struct loopdev_cxt *lc, const char *device)
        if (lc->fd >= 0)
                close(lc->fd);
        lc->fd = -1;
+       lc->mode = 0;
        lc->has_info = 0;
        *lc->device = '\0';
+       memset(&lc->info, 0, sizeof(lc->info));
 
        /* set new */
        if (device) {
@@ -92,6 +94,18 @@ int loopcxt_set_device(struct loopdev_cxt *lc, const char *device)
  *
  * Initilize loop handler.
  *
+ * We have two sets of the flags:
+ *
+ *     * LOOPDEV_FL_* flags control loopcxt_* API behavior
+ *
+ *     * LO_FLAGS_* are kernel flags used for LOOP_{SET,GET}_STAT64 ioctls
+ *
+ * Note about LOOPDEV_FL_{RDONLY,RDWR} flags. These flags are used for open(2)
+ * syscall to open loop device. By default is the device open read-only.
+ *
+ * The expection is loopcxt_setup_device(), where the device is open read-write
+ * if LO_FLAGS_READ_ONLY flags is not set (see loopcxt_set_flags()).
+ *
  * Returns: <0 on error, 0 on success.
  */
 int loopcxt_init(struct loopdev_cxt *lc, int flags)
@@ -183,14 +197,25 @@ struct sysfs_cxt *loopcxt_get_sysfs(struct loopdev_cxt *lc)
 int loopcxt_get_fd(struct loopdev_cxt *lc)
 {
        if (!lc || !*lc->device)
-               return -1;
+               return -EINVAL;
 
-       if (lc->fd < 0)
-               lc->fd = open(lc->device, lc->flags & LOOPDEV_FL_RDWR ?
-                               O_RDWR : O_RDONLY);
+       if (lc->fd < 0) {
+               lc->mode = lc->flags & LOOPDEV_FL_RDWR ? O_RDWR : O_RDONLY;
+               lc->fd = open(lc->device, lc->mode);
+       }
        return lc->fd;
 }
 
+int loopcxt_set_fd(struct loopdev_cxt *lc, int fd, int mode)
+{
+       if (!lc)
+               return -EINVAL;
+
+       lc->fd = fd;
+       lc->mode = mode;
+       return 0;
+}
+
 /*
  * @lc: context
  * @flags: LOOPITER_FL_* flags
@@ -481,6 +506,10 @@ char *loopcxt_get_backing_file(struct loopdev_cxt *lc)
        char *res = NULL;
 
        if (sysfs)
+               /*
+                * This is always preffered, the loop_info64
+                * has too small buffer for the filename.
+                */
                res = sysfs_strdup(sysfs, "loop/backing_file");
 
        if (!res && loopcxt_ioctl_enabled(lc)) {
@@ -570,6 +599,32 @@ int loopcxt_is_autoclear(struct loopdev_cxt *lc)
        return 0;
 }
 
+/*
+ * @lc: context
+ *
+ * Returns: 1 of the readonly flags is set.
+ */
+int loopcxt_is_readonly(struct loopdev_cxt *lc)
+{
+       struct sysfs_cxt *sysfs = loopcxt_get_sysfs(lc);
+
+       if (sysfs) {
+               int fl;
+               if (sysfs_read_int(sysfs, "ro", &fl) == 0)
+                       return fl;
+       }
+
+       if (loopcxt_ioctl_enabled(lc)) {
+               struct loop_info64 *lo = loopcxt_get_info(lc);
+               if (lo)
+                       return lo->lo_flags & LO_FLAGS_READ_ONLY;
+       }
+       return 0;
+}
+
+/*
+ * The setting is removed by loopcxt_set_device() loopcxt_next()!
+ */
 int loopcxt_set_offset(struct loopdev_cxt *lc, uint64_t offset)
 {
        if (!lc)
@@ -578,6 +633,9 @@ int loopcxt_set_offset(struct loopdev_cxt *lc, uint64_t offset)
        return 0;
 }
 
+/*
+ * The setting is removed by loopcxt_set_device() loopcxt_next()!
+ */
 int loopcxt_set_sizelimit(struct loopdev_cxt *lc, uint64_t sizelimit)
 {
        if (!lc)
@@ -590,6 +648,8 @@ int loopcxt_set_sizelimit(struct loopdev_cxt *lc, uint64_t sizelimit)
  * @lc: context
  * @flags: kernel LO_FLAGS_{READ_ONLY,USE_AOPS,AUTOCLEAR} flags
  *
+ * The setting is removed by loopcxt_set_device() loopcxt_next()!
+ *
  * Returns: 0 on success, <0 on error.
  */
 int loopcxt_set_flags(struct loopdev_cxt *lc, uint32_t flags)
@@ -604,6 +664,8 @@ int loopcxt_set_flags(struct loopdev_cxt *lc, uint32_t flags)
  * @lc: context
  * @filename: backing file path (the path will be canonicalized)
  *
+ * The setting is removed by loopcxt_set_device() loopcxt_next()!
+ *
  * Returns: 0 on success, <0 on error.
  */
 int loopcxt_set_backing_file(struct loopdev_cxt *lc, const char *filename)
@@ -634,9 +696,11 @@ static int digits_only(const char *s)
  * @encryption: encryption name / type (see lopsetup man page)
  * @password
  *
- * Note that the encyption functionality is deprecated an unmaintained. Use
+ * Note that the encryption functionality is deprecated an unmaintained. Use
  * cryptsetup (it also supports AES-loops).
  *
+ * The setting is removed by loopcxt_set_device() loopcxt_next()!
+ *
  * Returns: 0 on success, <0 on error.
  */
 int loopcxt_set_encryption(struct loopdev_cxt *lc,
@@ -676,15 +740,21 @@ int loopcxt_set_encryption(struct loopdev_cxt *lc,
  * Associate the current device (see loopcxt_{set,get}_device()) with
  * a file (see loopcxt_set_backing_file()).
  *
- * Default is open backing file and device in read-write mode, see
- * LOOPDEV_FL_{RDONLY,RDWR} and loopcxt_init(). The LO_FLAGS_READ_ONLY lo_flag
- * will be set automatically according to LOOPDEV_FL_ flags.
+ * The device is initialized read-write by default. If you want read-only
+ * device then set LO_FLAGS_READ_ONLY by loopcxt_set_flags(). The LOOPDEV_FL_*
+ * flags are ignored and modified according to LO_FLAGS_*.
+ *
+ * If the device is already open by loopcxt_get_fd() then this setup device
+ * function will re-open the device to fix read/write mode.
+ *
+ * The device is also initialized read-only if the backing file is not
+ * possible to open read-write (e.g. read-only FS).
  *
  * Returns: <0 on error, 0 on success.
  */
 int loopcxt_setup_device(struct loopdev_cxt *lc)
 {
-       int file_fd, dev_fd, mode, rc = -1;
+       int file_fd, dev_fd, mode = O_RDWR, rc = -1;
 
        if (!lc || !*lc->device || !lc->filename)
                return -EINVAL;
@@ -692,7 +762,8 @@ int loopcxt_setup_device(struct loopdev_cxt *lc)
        /*
         * Open backing file and device
         */
-       mode = (lc->flags & LOOPDEV_FL_RDONLY) ? O_RDONLY : O_RDWR;
+       if (lc->info.lo_flags & LO_FLAGS_READ_ONLY)
+               mode = O_RDONLY;
 
        if ((file_fd = open(lc->filename, mode)) < 0) {
                if (mode != O_RDONLY && (errno == EROFS || errno == EACCES))
@@ -702,11 +773,20 @@ int loopcxt_setup_device(struct loopdev_cxt *lc)
                        return -errno;
        }
 
+       if (lc->fd != -1 && lc->mode != mode) {
+               close(lc->fd);
+               lc->fd = -1;
+               lc->mode = 0;
+       }
+
        if (mode == O_RDONLY) {
-               lc->flags |= LOOPDEV_FL_RDONLY;
-               lc->info.lo_flags |= LO_FLAGS_READ_ONLY;
-       } else
-               lc->flags |= LOOPDEV_FL_RDWR;
+               lc->flags |= LOOPDEV_FL_RDONLY;                 /* open() mode */
+               lc->info.lo_flags |= LO_FLAGS_READ_ONLY;        /* kernel loopdev mode */
+       } else {
+               lc->flags |= LOOPDEV_FL_RDWR;                   /* open() mode */
+               lc->info.lo_flags &= ~LO_FLAGS_READ_ONLY;
+               lc->flags &= ~LOOPDEV_FL_RDONLY;
+       }
 
        dev_fd = loopcxt_get_fd(lc);
        if (dev_fd < 0) {
@@ -975,9 +1055,6 @@ static int test_loop_setup(const char *filename, const char *device)
 
        loopcxt_init(&lc, 0);
 
-       if (loopcxt_set_backing_file(&lc, filename))
-               err(EXIT_FAILURE, "failed to set backing file");
-
        if (device) {
                rc = loopcxt_set_device(&lc, device);
                if (rc)
@@ -992,6 +1069,9 @@ static int test_loop_setup(const char *filename, const char *device)
                        printf("Trying to use '%s'\n", loopcxt_get_device(&lc));
                }
 
+               if (loopcxt_set_backing_file(&lc, filename))
+                       err(EXIT_FAILURE, "failed to set backing file");
+
                rc = loopcxt_setup_device(&lc);
                if (rc == 0)
                        break;          /* success */